preferred embodiments of the present invention will be described hereinafter in detail with reference to the accompanying drawings . a communication system according to a first embodiment of the present invention starts a communication by causing a switchboard to transmit information on addresses of switchboard terminals other than a switchboard terminal of the switchboard , and the switchboard terminal that has received the addresses to select a communication partner from among the switchboard terminals at the received addresses , and to pass the address of the selected switchboard terminal to independent general - purpose p2p communication software incorporated in the switchboard terminal . furthermore , while the switchboard terminal is holding a voice communication , a communication starts by passing address information on a voice output destination to the general - purpose communication software . if the switchboard terminal separates from the p2p general - purpose communication software and differs in address , a communication starts by registering information for coupling them with each other in the switchboard and passing the information to the switchboard terminal in response to a request from the switchboard terminal . moreover , if the switchboard terminal is holding a voice conference , a communication starts by passing address information on a voice conference partner to the switchboard terminal . a configuration of the communication system using voice lines ( i . e ., an internal voice line and an external voice line ) and a lan line in an office as shown in fig1 will be described . it is assumed that a communication method realized by the p2p communication software is a video communication . in the office , a voice switchboard 101 ( hereinafter , simply “ switchboard ”) switching voice communication , a voice and video terminal 102 used by a user a and connected to a lan line , a voice and video terminal 103 used by a user b and connected to the lan line , a video terminal 104 used by a user c and connected to the lan line , a voice terminal 107 connected to a voice internal line , a voice terminal 105 used by a user d and connected to the lan line , a video terminal 106 connected to the lan line , a cti ( computer telephony integration ) server 109 connected to the switchboard 101 and realizing cti , and a presence server 110 managing and notifying status information ( presence ) of the terminals 102 to 107 are present . further , the switchboard 101 is connected to a voice communication network 108 via a voice external line . in this way , the switchboard 101 is connected to the voice communication network 108 and the terminals 102 to 107 , and controls connection of voice communications held by the terminals 102 to 107 . the cti server 109 mediates a communication between cti client software mounted in each of the terminals 102 to 106 connected to the lan line and the switchboard 101 . the presence server 110 communicates with the switchboard 101 and the terminals 102 to 106 connected to the lan line , constantly updates and holds the status information ( presences ) of the terminals 102 to 107 , and transmits a notification to each of the terminals 102 to 106 and the switchboard 101 in response to a request . referring now to fig2 , operations performed by respective constituent elements of each of the terminals 102 to 107 will be outlined . a user interface (“ i / f ”) 201 receives input signals from a keyboard , a mouse or the like and outputs video signals to a display . a voice source i / f 202 transmits and receives voice data to and from a voice source 208 connected to the voice source i / f 202 . a voice internal line i / f 203 transmits and receives signals to and from the voice communication line . a lan line i / f 204 transmits and receives signals to and from the lan line . a cpu 205 controls entirety of the terminal . a memory 206 is used as a work area when software or data necessary to control the terminal is used . a terminal software 211 is software stored in the memory 206 and executed by the cpu 205 . a video i / f 209 receives signals input from a video camera 210 connected to the video i / f 209 . referring to fig3 , operations performed by respective constituent elements of the switchboard 101 will be outlined . a voice internal line i / f 301 transmits and receives signals to and from the voice communication line . a lan line i / f 302 transmits and receives signals to and from the lan line . a voice external line i / f 303 transmits and receives signals to and from the voice external line . a cpu 304 controls entirety of the switchboard 101 . a memory 305 is used as a work area when software or data necessary to control the switchboard 101 is used . a database 306 is an area for holding various setting data stored in the memory 305 . fig4 is a schematic diagram showing a module configuration of software 211 stored in the memory 206 in each of the voice and video terminals 102 and 103 . switchboard terminal software 402 and video communication software 408 are application software operating on an os ( operating system ) 401 . the switchboard terminal software 402 is constituted by various software modules . a switchboard i / f 403 controls communication with the switchboard 101 . a voice communication control unit 404 controls voice signal communication by communicating with the voice source i / f 202 , the voice internal line i / f 203 , and the lan line i / f 204 . a cti server i / f 405 controls communication with the cti server 109 by communicating with the lan line i / f 204 . a presence server i / f 406 controls communication with the presence server 110 by communicating with the lan line i / f 204 . user setting data 407 stores therein a user id and a password of the user of the terminal , information on a current communication partner and the like . the video communication software 408 is a general - purpose p2p communication software and has a video communication capability to start communication between the terminals in which the video communication software is mounted , to transmit and receive video data , and to perform a communication end processing in the first embodiment . the video communication software 408 includes a function of receiving address information on a communication partner , i . e ., the other software mounted in the same terminal , and starting a communication with the partner according to the address information . fig5 shows an example of contents of the database 306 stored in the memory 305 of the switchboard 101 . in a “ switchboard user id ” area 501 , id information on each of the users using the switchboard 101 is stored . in a “ switchboard user password ” area 502 , a password corresponding to the user id is stored . in a “ possible communication method : address : port ” area 503 , a possible communication method of the terminal used by each user , an address of the terminal , and a port number used by the communication method in the terminal are stored . if the terminal supports a plurality of communication methods , a plurality of information is stored in the “ possible communication method : address : port ” area 503 . in a “ communication partner user id ” area 504 , a user id or an external line number of a communication partner is stored if the user is holding a communication . in an “ external line ” area 505 , the number of each voice external line connected to the switchboard 101 is stored . in a “ communication partner number ” area 506 , a telephone number of the communication partner on a voice external line having the external line number is stored . fig6 shows an example of contents of the terminal software 211 stored in the memory 206 of each of the voice and video terminals 102 and 103 . in a “ switchboard user id ” area 601 , a switchboard user id of a user using the terminal 102 or 103 is stored . in a “ switchboard user password ” area 602 , a password corresponding to the user id is stored . in a “ possible communication method : address : port ” area 603 , a possible communicate method of the terminal , the address of the terminal , and the port number used by the communication method in the terminal are stored . if the terminal supports a plurality of communication methods , a plurality of information is stored per user id . if the terminal is connected to the voice line , an internal line number is stored in place of the address and the port number . a “ communication partner ” area 604 is an area in which information on the communication partner is stored during a voice or video communication of the terminal . namely , in the “ communication partner ” area 604 , a user id , an address , and a port number of the communication partner are stored . if the communication partner is a terminal that does not include a lan line i / f and that is connected to the voice line or a terminal that is connected to the voice external line , an internal line number or an external line number is stored in the “ communication partner ” area 604 in place of the address , and the port number of the communication partner . in a “ communication destination port initial value ” area 605 , a default destination port used if the communication port of the communication partner is unknown for every communication method is stored . first , an instance in which the user a starts a video communication with the user b while the user a is not on the phone will be described with reference to the flowchart of fig7 . it is assumed herein that only the address and the port for the voice communication are stored in the “ possible communication method : address : port ” area 603 in the terminal software 211 stored in the memory 206 of each of the voice and video terminals 102 and 103 . it is also assumed that the terminal configuration of each of the voice and video terminals 102 and 103 is such that the voice internal line i / f 203 is not present in the configuration of the voice and video terminal shown in fig2 . first , the user a input a user id and a password using the keyboard and display 207 of the voice and video terminal 102 . in response to the input , the cpu 205 and the switchboard terminal software 402 operating in the memory 206 receive information on the user id and the password of the user a via the user i / f 201 and the os 401 , respectively . further , the input user id is stored in the “ switchboard user id ” area 601 and the password is stored in the “ switchboard user password ” area 602 . the user id and the password as well as the information stored in the “ possible communication method : address : port ” area 603 of the voice and video terminal 102 are passed to the os 401 via the switchboard i / f 403 , and transmitted to the switchboard 101 via the lan i / f 204 . when receiving the information via the lan line i / f 302 , the switchboard 101 searches the received user id from the areas 501 in the database 306 , and checks whether the password stored in the area 502 corresponding to the hit area 501 is identical with the received password . if the switchboard 101 confirms that the both passwords are identical , the switchboard 101 stores the received information of “ possible communication method : address : port ” in the corresponding area 503 . likewise , the user b registers the voice and video terminal 103 in the switchboard 101 ( step 701 ). the user a performs an operation for calling a video communication partner list using the keyboard and display 207 of the voice and video terminal 102 . in response to the operation , a user list disclosure request is passed from the switchboard terminal software 402 to the os 401 via the switchboard i / f 403 , and transmitted to the switchboard 101 via the lan i / f 204 . when receiving the information via the lan line i / f 302 , the switchboard 101 extracts all the information stored in “ switchboard user id ” areas 501 and “ possible communication method : address : port ” areas 503 corresponding to all the users in the database 306 included in the switchboard 101 , and transmits the information to the voice and video terminal 102 . the switchboard i / f 403 of the switchboard terminal software 402 in the voice and video terminal 102 receives the information via the lan line i / f 204 and the os 401 , and the voice and video terminal 102 displays the information on the display 207 via the user i / f 201 ( step 702 ). the user a performs an operation for selecting the video communication partner using the keyboard and display 207 of the voice and video terminal 102 . in response to the operation , the user id of the selected video communication partner is passed from the switchboard terminal software 402 to the os 401 via the switchboard i / f 403 , and transmitted to the switchboard 101 via the lan line i / f 204 . when receiving the information via the lan line i / f 302 , the switchboard 101 searches the received user id from the “ switchboard user id ” areas 501 in the database 306 of the switchboard 101 , extracts information described in the “ possible communication method : address : port ” area 503 corresponding to the hit record ( area 501 ), and transmits the extracted information to the voice and video terminal 102 . the switchboard i / f 403 of the switchboard terminal software 402 in the voice and video terminal 102 receives the information via the lan line i / f 204 and the os 401 ( step 703 ). the switchboard terminal software 402 checks the received possible communication method , address , and port to confirm whether video communication is present in the area 603 . in the first embodiment , since the address and the port for the video communication are not described in the area 603 , the switchboard terminal software 402 extracts only the address for the voice communication , extracts a video communication port ( port 101 ) described in the “ communication destination port initial value ” area 605 as the port , and passes the address and the port to the video communication software 408 . at the same time , the switchboard terminal software 402 writes contents of the information in the “ communication partner ” area 604 in the user setting data 211 as video communication partner information ( step 704 ). the video communication software 408 starts a video communication by setting the received address and port as the communication destination ( step 705 ). in the first embodiment , it is assumed that only the address and the port for the voice communication are stored in the “ possible communication method : address : port ” area 603 in the terminal software 211 stored in the memory 206 of each of the voice and video terminals 102 and 103 . alternatively , not only the address and the port for the voice communication but also the address and the port for the video communication may be stored in the “ possible communication method : address : port ” area 603 . in this alternative , the user a can confirm whether the communication partner is a video - communicable terminal in advance at the step 703 . moreover , at the step 704 , the switchboard terminal software 402 passes the address and the port for the video communication among the information of the possible communication method , address , and port received from the switchboard 101 to the video communication software 408 . it is thereby possible for the terminal 102 to flexibly set the video communication port . furthermore , in the first embodiment , the p2p communication software has been described while taking that for the video communication as an example . however , as long as the software enables communication only by receiving the address and the port , the software is not limited to the video communication software . by changing the video communication software 408 to arbitrary p2p communication software , the present invention is applicable to various communication methods such as mail communication , instant message communication , file sharing communication , whiteboard sharing communication , and application sharing communication . in the first embodiment , it is necessary for each user to manually select the video communication partner by operating the terminal of the user . however , during a conversation , the communication partner may be automatically selected so as to be able to start a video communication . an instance of automatically selecting the communication partner will be described with reference to the flowchart of fig8 . it is assumed herein that the address and the port for the voice communication and those for the video communication are stored in the “ possible communication method : address : port ” area 603 of each of the voice and video terminals 102 and 103 . a step 801 is the same as the step 701 according to the first embodiment . the voice and video terminal 102 transmits signals to the voice and video terminal 103 using the voice internal line , thereby establishing a voice communication . at this time , the address and the communication method ( voice communication ) of the voice signal destination ( i . e ., the terminal of the voice communication partner ) are stored in the “ communication partner ” area 604 in the user setting data 211 . further , the switchboard software 402 writes the user id of the communication partner in the “ communication partner user id ” area 504 corresponding to each user in the database 306 of the switchboard 101 ( step 802 ). the user a performs an operation for staring a video communication with the current voice communication partner using the keyboard and display 207 of the voice and video terminal 102 . in response to the operation , a current communication partner information request is passed from the switchboard terminal software 402 to the os 401 via the switchboard i / f 403 , and transmitted to the switchboard 101 via the lan line i / f 204 . when receiving the current communication partner information request via the lan line i / f 302 , the switchboard 101 reads information described in the “ communication partner user id ” area 504 corresponding to the user a in the database 306 , and searches the “ switchboard user id ” area 501 corresponding to the user id described in the area 504 . further , the switchboard 101 extracts the possible communication method , address , and port from the “ possible communication method : address : port ” area 503 corresponding to the hit area 501 , and transmits the extracted information to the voice and video terminal 102 . the switchboard i / f 403 of the switchboard terminal software 402 of the voice and video terminal 102 receives the information via the lan line i / f 204 and the os 401 ( step 803 ). the switchboard terminal software 402 checks the received possible communication method , address , and port , and confirms whether the video communication is present in the “ possible communication method : address : port ” area 503 . if the video communication is present , the switchboard terminal software 402 passes the address and the port for the video communication to the video communication software 408 , and at the same time , writes contents of the address and the port for the video communication in the “ communication partner ” area 604 in the user setting data 211 stored in the voice and video terminal 102 as the video communication partner information ( step 804 ). the video communication software 408 starts a video communication while setting the received address and port as the communication destination ( step 805 ). in the second embodiment , the switchboard 101 is inquired about the communication partner information at the step 803 . alternatively , if the communication partner information stored in the terminal 102 is used , there is no need to inquire the switchboard 101 about the communication partner information . in this alternative , the switchboard terminal software 402 reads the information described in the “ communication partner ” area 604 in the user setting data 211 at the step 803 . the switchboard terminal software 402 passes the address and the port described in the area 604 to the video communication software 408 at the step 804 . it is thereby possible to control the video communication without using the switchboard 101 at all . in the preceding first and second embodiments , the voice terminal is identical with the video terminal and the voice and video terminals have the same address . however , the video terminal and the voice and video terminals may be different terminals . an instance in which the video terminal and the voice and video terminals are different will be described with reference to the flowchart of fig9 . it is assumed herein that the address and the port for the video communication are stored in the “ possible communication method : address : port ” area 603 of each of the video terminals 104 and 106 , that the address and the port for the voice communication are stored in the “ possible communication method : address : port ” area 603 of the video terminal 105 , and that the “ possible communication method : address : port ” area 603 of the voice terminal 107 is blank . it is also assumed that the internal line number of the voice terminal 107 is set in the “ possible communication method : address : port ” area 503 corresponding to the user c described in the “ user id area ” 501 of the database 306 of the switchboard 101 , as the address for the voice communication in advance , and that no port is described in the same “ possible communication method : address : port ” area 503 . it is further assumed that the voice terminal 107 is already activated and on standby . moreover , it is assumed that the terminal configuration of each of the video terminals 104 and 106 is such that the voice internal line i / f 203 and the voice source i / f 202 are not present in the configuration of the voice and video terminal shown in fig2 , the terminal configuration of the voice terminal 105 is such that the voice internal line i / f 203 and the video i / f 209 are not present in the configuration of the voice and video terminal shown in fig2 , and that the terminal configuration of the voice terminal 107 is such that the video i / f 209 and the lan line i / f 204 are not present in the configuration of the voice and video terminal shown in fig2 . first , the user c registers the video terminal 104 and the voice terminal 107 in the switchboard 101 , and the user d registers the voice terminal 105 and the video terminal 106 in the switchboard 101 using their respective user ids and passwords , respectively through procedures similar to that of the step 701 in the first embodiment ( step 901 ). the voice terminal 107 transmits signals to the voice terminal 105 using the voice internal line , thereby establishing a voice communication . at this time , the address and the communication method ( voice communication ) of the voice signal destination ( i . e ., the terminal of the voice communication partner ) are stored in the “ communication partner ” area 604 in the user setting data 211 stored in the terminal 107 . further , the switchboard software 402 writes the user id of the communication partner in the “ communication partner user id ” area 504 corresponding to each of the users c and d in the database 306 of the switchboard 101 when establishing the voice communication between them ( step 902 ). the user c performs an operation for staring a video communication with the current voice communication partner using the keyboard and display 207 of the voice and video terminal 104 ( step 903 ). in response to the operation , the switchboard terminal software 402 passes a current communication partner information request to the os 401 via the switchboard i / f 403 , and the current communication partner information request is transmitted to the switchboard 101 via the lan line i / f 204 . when receiving the current communication partner information request via the lan line i / f 302 , the switchboard 101 reads information described in the “ communication partner user id ” area 504 corresponding to the user c in the database 306 , and searches the “ switchboard user id ” area 501 corresponding to the user id described in the area 504 . further , the switchboard 101 extracts the possible communication method , address , and port from the “ possible communication method : address : port ” area 503 corresponding to the hit area 501 , and transmits the extracted information to the video terminal 104 . the switchboard i / f 403 of the switchboard terminal software 402 of the video terminal 104 receives the information via the lan line i / f 204 and the os 401 ( step 904 ). the switchboard terminal software 402 checks the received possible communication method , address , and port , and confirms whether the video communication is present in the “ possible communication method : address : port ” area 503 . if the video communication is present , the switchboard terminal software 402 passes the address and the port for the video communication to the video communication software 408 , and at the same time , writes contents of the address and the port for the video communication in the “ communication partner ” area 604 in the user setting data 211 stored in the video terminal 104 as the video communication partner information ( step 905 ). the video communication software 408 starts a video communication while setting the received address and port as the communication destination ( step 906 ). in the preceding first to third embodiments , the address and the port of the communication partner are passed to the video communication software 408 at the start of the video communication , and the video communication software 408 is entrusted with the subsequent video communication control . due to this , even if the voice communication is finished , the user is forced to manually instruct the video communication software 408 for the video communication . alternatively , the switchboard terminal software 402 may detect end of the voice communication using the cti server i / f 405 , and instruct the video communication software 408 to finish a video communication , thereby automatically finishing the video communication simultaneously with the end of the voice communication . an instance of automatically finishing the video communication simultaneously with the end of the voice communication using the cti server i / f 405 will be described with reference to the flowchart of fig1 . it is assumed herein that the switchboard terminal software 402 of the video terminal 104 is connected to the cti server 109 via the cti server i / f 405 and that the voice terminal 107 is registered as a cti control target . it is also assumed that the cti server 109 acquires a status ( presence ) of the voice terminal 107 by communicating with the voice switchboard 101 and transmits the status information to the cti server i / f 405 of the video terminal 104 . further , it is assumed that all the procedures at the steps 901 to 906 are already carried out . first , a voice communication between the voice terminal 107 of the user c and the voice terminal 105 of the user d is finished ( step 1001 ). the switchboard 101 notifies the cti server 109 of the end of the voice communication between the voice terminals 105 and 107 via the lan line i / f 302 simultaneously with the end of the voice communication . the cti server 109 notifies the cti server i / f 405 of the video terminal 104 that the voice terminal 107 finishes the voice communication ( step 1002 ). the switchboard terminal software 402 of the video terminal 104 reads video communication partner information from the “ communication partner ” area 604 corresponding to the user c in the user setting data 211 , deletes the information from the area 604 , and then passes a video communication end instruction as well as the information to the video communication software 408 ( step 1003 ). the video communication software 408 finishes the video communication for which the received address and port are set as the communication destination ( step 1004 ). in the fourth embodiment , the switchboard terminal software 402 detects the end of the voice communication by using the cti server i / f 405 . alternatively , the switchboard terminal software 402 may detect the end of the voice communication using the presence server i / f 406 , and instruct the video communication software 408 to finish a video communication , thereby automatically finishing the video communication simultaneously with the end of the voice communication . an instance of automatically finishing the video communication simultaneously with the end of the voice communication using the presence server i / f 406 will be described with reference to the flowchart of fig1 . it is assumed herein that the switchboard terminal software 402 of the video terminal 104 is connected to the presence server 110 via the presence server i / f 406 and that the voice terminal 107 is registered as a presence watching target . it is also assumed that the presence server 110 acquires a status ( presence ) of the voice terminal 107 by communicating with the switchboard 101 and transmits the status information to the presence server i / f 406 of the video terminal 104 . further , it is assumed that all the procedures at the steps 901 to 906 are already carried out . first , a voice communication between the voice terminal 107 of the user c and the voice terminal 105 of the user d is finished ( step 1101 ). the switchboard 101 notifies the presence server 110 that the presence of the voice terminal 107 changes from a state of holding a voice communication to a standby state , via the lan line i / f 302 simultaneously with the end of the voice communication . the presence server 110 notifies the presence server i / f 406 of the video terminal 104 that the voice terminal 107 finishes the voice communication ( step 1102 ). the switchboard terminal software 402 of the video terminal 104 regards the information as the end of the voice communication , reads video communication partner information from the “ communication partner ” area 604 corresponding to the user c in the user setting data 211 , deletes the information from the area 604 , and then passes a video communication end instruction as well as the information to the video communication software 408 ( step 1103 ). the video communication software 408 finishes the video communication for which the received address and port are set as the communication destination ( step 1104 ). in the preceding first to fifth embodiments , one - to - one voice or video communication is held . alternatively , a video conference communication may be held by interlocking the voice or video communication with a voice conference by a plurality of terminals . an instance of holding a video conference communication will be described with reference to the flowchart of fig1 . it is assumed herein that the address and the port for the voice communication and the address and the port for the video communication are stored in the “ possible communication method : address : port ” area 603 of the voice and video terminal 102 , that the address and the port for the video communication are stored in the “ possible communication method : address : port ” area 603 of each of the video terminals 104 and 106 , that the address and the port for the voice communication are stored in the “ possible communication method : address : port ” area 603 of the voice terminal 105 , and that the “ possible communication method : address : port ” area 603 of the voice terminal 107 is blank . it is also assumed that the internal line number of the voice terminal 107 is set in the “ possible communication method : address : port ” area 503 corresponding to the user c described in the “ user id area ” 501 of the database 306 of the switchboard 101 , as the address for the voice communication in advance , and that no port is described in the same “ possible communication method : address : port ” area 503 . it is further assumed that the voice terminal 107 is already activated and on standby . further , it is assumed that the video communication software 408 can simultaneously hold video communications with a plurality of communication partners . moreover , it is assumed that the terminal configuration of each of the video terminals 104 and 106 is such that the voice internal line i / f 203 and the voice source i / f 202 are not present in the configuration of the voice and video terminal shown in fig2 , the terminal configuration of the voice terminal 105 is such that the voice internal line i / f 203 and the video i / f 209 are not present in the configuration of the voice and video terminal shown in fig2 , and that the terminal configuration of the voice terminal 107 is such that the video i / f 209 and the lan line i / f 204 are not present in the configuration of the voice and video terminal shown in fig2 . first , the user a registers the voice and video terminal 102 , the user c registers the video terminal 104 and the voice terminal 107 , and the user d registers the voice terminal 105 and the video terminal 106 in the switchboard 101 using their respective user ids and passwords , respectively through procedures similar to that of the step 701 in the first embodiment ( step 1201 ). a conference communication is established among the voice and video terminal 102 , the voice terminal 107 , and the voice terminal 105 . at this time , the addresses and the communication methods ( voice communication ) of the voice signal destinations ( i . e ., the terminals of the voice communication partners ) are stored in the “ communication partner ” area 604 in the user setting data 211 in each of the terminals 102 , 105 , and 107 . further , the switchboard software 402 of each of the terminals 102 , 105 , and 107 writes the user ids of the communication partners in the “ communication partner user id ” area 504 corresponding to each of the users a , c , and d in the database 306 of the switchboard 101 when the conference communication is held among them ( step 1202 ). the user c performs an operation for staring a video communication with the current voice communication partners using the keyboard and display 207 of the voice and video terminal 104 ( step 1203 ). in response to the operation , the switchboard terminal software 402 of the voice and video terminal 104 passes a current communication partner information request to the os 401 via the switchboard i / f 403 , and the current communication partner information request is transmitted to the switchboard 101 via the lan line i / f 204 . when receiving the current communication partner information request via the lan line i / f 302 , the switchboard 101 reads information described in the “ communication partner user id ” area 504 corresponding to the user c in the database 306 , and searches a plurality of “ switchboard user id ” areas 501 corresponding to the user ids described in the areas 504 , respectively . further , the switchboard 101 extracts the possible communication methods , addresses , and ports from the “ possible communication method : address : port ” areas 503 corresponding to the hit plural areas 501 , and transmits all the extracted information as well as the user ids to the video terminal 104 . the switchboard i / f 403 of the switchboard terminal software 402 of the video terminal 104 receives the information via the lan line i / f 204 and the os 401 ( step 1204 ). the switchboard terminal software 402 checks all the received possible communication methods , addresses , and ports , and confirms whether the video communication is present in each of the “ possible communication method : address : port ” areas 503 . if the video communication is present in each of the “ possible communication method : address : port ” areas 503 , the switchboard terminal software 402 displays the user ids of a plurality of video - communicable video communication partner candidates on the display 207 via the user i / f 201 . thereafter , the user c performs an operation for selecting an arbitrary video communication partner from among the displayed user ids using the keyboard and display 207 of the video terminal 104 ( step 1205 ). in response to the selection operation , the switchboard terminal software 402 passes the address and the port of the selected user id for the video communication to the video communication software 408 , and at the same time , writes contents of the address and the port for the video communication in the “ communication partner ” area 604 in the user setting data 604 stored in the video terminal 104 as the video communication partner information ( step 1206 ). the video communication software 408 starts a video communication while setting the received address and port as the communication destination ( step 1207 ). the user c can additionally perform the operation for selecting a video communication partner from among the displayed user ids using the keyboard and display 207 of the video terminal 104 if the user wants to hold a video communication with another user . in this case , the procedures at the steps 1206 to 1208 are repeatedly carried out whenever the selection operation is performed ( step 1208 ). although the exemplary embodiments of the present invention have been described in detail , it should be understood that various changes , substitutions and alternatives can be made therein without departing from the sprit and scope of the invention as defined by the appended claims . further , it is the inventor &# 39 ; s intent to retain all equivalents of the claimed invention even if the claims are amended during prosecution .