fig3 depicts a schematic diagram of telecommunications system 300 , in accordance with an illustrative embodiment of the present invention . telecommunications system 300 comprises telecommunications network 105 , private branch exchanges 304 - 1 through 304 - p , where p is an integer greater than one , network 305 , off - premises affiliated wireless terminal 301 , telecommunications terminal 306 , and server 310 , interconnected as shown . private branch exchanges 304 - 1 through 304 - p are capable of providing all the functionality of private branch exchange 104 of the prior art , of transmitting and receiving signals among one another via network 305 , and of performing the functions described below and with respect to fig5 through 14 . as will be appreciated by those skilled in the art , in some embodiments of the present invention private branch exchanges 304 - 1 through 304 - p might be instances of some other type of routing or switching element , rather than what is historically connoted by the terms “ private branch exchange ” or “ pbx ,” and it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention that comprise such alternative routing or switching elements . network 305 is capable of transporting signals among private branch exchanges 304 - 1 through 304 - p , of transmitting and receiving signals via telecommunications terminal 105 , and of transmitting signals to and receiving signals from server 310 , in well - known fashion . in some embodiments network 305 might be a public network ( e . g ., the pstn , the internet , etc . ), while in some other embodiments network 305 might be a private network ( e . g ., leased lines , a virtual private network [ vpn ] over the internet , etc . ), while in still some other embodiments network 305 might be a combination of public and private networks . off - premises affiliated wireless terminal 301 is a wireless telecommunications terminal that is affiliated with some on - premises terminal of one of private branch exchanges 304 - 1 through 304 - p . the particular private branch exchange and on - premises terminal with which terminal 301 is affiliated is immaterial — it matters only that terminal 301 is affiliated with some on - premises terminal of the organization . in accordance with the illustrative embodiment , affiliated wireless terminal 301 is capable of storing the internet protocol address of server 310 , and of transmitting signals to and receiving signals from server 310 . in addition , affiliated wireless terminal 301 is capable of accessing the contents of a table of information about the organization &# 39 ; s private branch exchanges ( e . g ., their phone numbers , their geo - locations , etc . )— such as illustrative table 400 shown in fig4 — and of performing the functions described below and with respect to fig5 through 14 . as will be appreciated by those skilled in the art , in some embodiments illustrative table 400 might be stored locally at affiliated wireless terminal 301 , while in some other embodiments illustrative table 400 might be stored elsewhere ( e . g ., server 310 , etc .) and accessed remotely by terminal 301 . in either case , it will be clear to those skilled in the art , after reading this disclosure , how to make and use affiliated wireless terminal 301 . server 310 is a data - processing system that is capable of transmitting and receiving signals via telecommunications network 105 and network 305 , of populating and updating illustrative table 400 , and of performing the functions described below and with respect to fig5 through 14 . fig5 depicts the transmission of signals among elements of telecommunications system 300 during registration of affiliated wireless terminal 301 in response to an identity change at terminal 301 , in accordance with the first illustrative embodiment of the present invention . in particular , fig5 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange 304 - i , and visitor private branch exchange 304 - j . as is the case for subsequent fig6 through 14 , fig5 is logical in nature ; i . e ., it depicts the transmission of signals among elements of telecommunications system 300 in an abstract , rather than physical , fashion , and does not include a depiction of any particular conduits of transmission ( e . g ., network 105 , network 305 , etc .) or intermediate nodes that might be present in the actual physical transmission path ( e . g ., a session initiation protocol server for a voice over internet protocol call , etc .). it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig5 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig5 can be performed simultaneously or in a different order than that depicted . signal transmissions are depicted in fig5 as arrows between nodes , where the temporal sequence of transmissions is in accordance with the arrows &# 39 ; numerical labels , in ascending order . at signal transmission 501 , one or more enterprise private branch exchanges 304 transmit a subscription request to server 310 requesting future updates on information including the identities of affiliated wireless terminals , the geo - locations of affiliated wireless terminals , and least - cost route information . ( for convenience , fig5 shows two such signal subscription requests 501 , labeled 501 - 1 and 501 - 2 , submitted by home private branch exchange 304 - i and visitor private branch exchange 304 - j , respectively .) as will be appreciated by those skilled in the art , the transmission of subscription requests by a plurality of enterprise private branch exchanges might not necessarily occur simultaneously . at signal transmission 502 , affiliated wireless terminal 301 transmits to server 310 an indication of its current geo - location ( e . g . gps coordinates , current cell id , etc . ), and an indication of a change in its identity ( e . g ., its user has inserted a new sim card , etc .). after receiving signal transmission 502 , server 310 determines which of the enterprise &# 39 ; s private branch exchange is “ closest ” to the terminal ( i . e ., the identity of visitor private branch exchange 304 - j , which is already depicted in fig5 ) and updates least - cost routes , if necessary . at signal transmission 503 , server 310 notifies wireless terminal 301 of the identity of visitor private branch exchange 304 - j for subsequent calls made from the terminal . at signal transmission 504 , server 310 notifies home private branch exchange 304 - i of terminal 301 &# 39 ; s new identity , and of any updated least - cost route information . in response to signal transmission 504 , home private branch exchange 304 - i accordingly updates its table mapping off - premises telephone numbers to on - premises telephone numbers . at signal transmission 505 , server 310 notifies visitor private branch exchange 304 - j of the presence of wireless terminal 301 and any updated least - cost route information . fig6 depicts the transmission of signals among elements of telecommunications system 300 during registration of affiliated wireless terminal 301 in response to a geo - locational change for terminal 301 , accordance with the first illustrative embodiment of the present invention . in particular , fig6 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig6 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig6 can be performed simultaneously or in a different order than that depicted . at signal transmission 601 , one or more enterprise private branch exchanges 304 transmit a subscription request to server 310 requesting future updates on information including the identities of affiliated wireless terminals , the geo - locations of affiliated wireless terminals , and least - cost route information . ( for convenience , fig6 shows two such signal subscription requests 601 , labeled 601 - 1 and 601 - 2 , submitted by home private branch exchange 304 - i and visitor private branch exchange 304 - j , respectively .) as will be appreciated by those skilled in the art , the transmission of subscription requests by a plurality of enterprise private branch exchanges might not necessarily occur simultaneously . at signal transmission 602 , affiliated wireless terminal 301 transmits to server 310 an indication of its current geo - location ( e . g . gps coordinates , current cell id , etc . ), in well - known fashion . after receiving signal transmission 602 , server 310 determines the identity of visitor private branch exchange 304 - j ( already depicted in fig6 ), and updates least - cost routes , if necessary . at signal transmission 603 , server 310 notifies wireless terminal 301 of the identity of visitor private branch exchange 304 - j for subsequent calls made from the terminal . at signal transmission 604 , server 310 notifies home private branch exchange 304 - i of terminal 301 &# 39 ; s new identity , and of any updated least - cost route information . at signal transmission 605 , server 310 notifies visitor private branch exchange 304 - j of the presence of wireless terminal 301 and of any updated least - cost route information . fig7 depicts the transmission of signals among elements of telecommunications system 300 when affiliated wireless terminal 301 places a call , in accordance with the first illustrative embodiment of the present invention . in particular , fig7 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange 304 - i , and visitor private branch exchange 304 - j . it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig7 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig7 can be performed simultaneously or in a different order than that depicted . at signal transmission 701 , affiliated wireless terminal 301 places a call by transmitting a signal to visitor private branch exchange 304 - j that specifies a particular destination ( e . g ., the telephone number of another wireless terminal , etc .) and instructs the pbx to route the call to the specified destination . at signal transmission 702 , visitor private branch exchange 304 - j routes the call to home private branch exchange 304 - i , in well - known fashion . at signal transmission 703 , home private branch exchange 304 - i extends the call to the destination , in well - known fashion . as will be appreciated by those skilled in the art , the call might be extended to a destination whose telephone number is in the address space of home private branch exchange 304 - i , or an extension within the address space of home private branch exchange 304 - i that does not correspond to any terminal , or might be routed externally to a terminal whose telephone number is outside the address space of home private branch exchange 304 - i ( as depicted in fig7 ). fig8 depicts the transmission of signals among elements of telecommunications system 300 when affiliated wireless terminal 301 receives a call that is directed to its associated on - premises terminal , in accordance with the first illustrative embodiment of the present invention . in particular , fig8 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange 304 - i , and visitor private branch exchange 304 - j . it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig8 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig8 can be performed simultaneously or in a different order than that depicted . at signal transmission 801 , home private branch exchange 304 - i receives a call that is directed to the on - premises telephone number associated with affiliated wireless terminal 301 . as will be appreciated by those skilled in the art , the call might originate from a terminal whose telephone number is in the address space of home private branch exchange 304 - i , or might originate from a terminal whose telephone number is outside the address space of home private branch exchange 304 - i ( as depicted in fig8 ). at signal transmission 802 , home private branch exchange 304 - i routes the call to visitor private branch exchange 304 - j , in well - known fashion . at signal transmission 803 , visitor private branch exchange 304 - j extends the call to affiliated wireless terminal 301 , in well - known fashion . fig9 depicts the transmission of signals among elements of telecommunications system 300 during registration of affiliated wireless terminal 301 in response to an identity change at terminal 301 , in accordance with both the second and third illustrative embodiments of the present invention . in particular , fig9 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange 304 - i , and visitor private branch exchange 304 - j . it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig9 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig9 can be performed simultaneously or in a different order than that depicted . at signal transmission 901 , affiliated wireless terminal 301 transmits to server 310 an indication of its current geo - location ( e . g . gps coordinates , current cell id , etc . ), and an indication of a change in its identity ( e . g ., its user has inserted a new sim card , etc .). after receiving signal transmission 901 , server 310 determines which of the enterprise &# 39 ; s private branch exchange is “ closest ” to the terminal ( i . e ., the identity of visitor private branch exchange 304 - j , which is already depicted in fig9 ) and updates least - cost routes , if necessary . at signal transmission 902 , server 310 notifies wireless terminal 301 of the identity of visitor private branch exchange 304 - j for subsequent calls made from the terminal . at signal transmission 903 , server 310 notifies home private branch exchange 304 - i of terminal 301 &# 39 ; s new identity . in response to signal transmission 903 , home private branch exchange 304 - i accordingly updates its table mapping off - premises telephone numbers to on - premises telephone numbers . fig1 depicts the transmission of signals among elements of telecommunications system 300 during registration of affiliated wireless terminal 301 in response to a geo - locational change for terminal 301 , in accordance with both the second and third illustrative embodiments of the present invention . in particular , fig1 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange 304 - i , and visitor private branch exchange 304 - j . it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig1 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig1 can be performed simultaneously or in a different order than that depicted . at signal transmission 1001 , affiliated wireless terminal 301 transmits to server 310 an indication of its current geo - location ( e . g . gps coordinates , current cell id , etc . ), in well - known fashion . after receiving signal transmission 1001 , server 310 determines which of the enterprise &# 39 ; s private branch exchange is “ closest ” to the terminal ( i . e ., the identity of visitor private branch exchange 304 - j , which is already depicted in fig1 ) and updates least - cost routes , if necessary . at signal transmission 1002 , server 310 notifies wireless terminal 301 of the identity of visitor private branch exchange 304 - j for subsequent calls made from the terminal . at signal transmission 1003 , server 310 notifies home private branch exchange 304 - i of terminal 301 &# 39 ; s new identity . in response to signal transmission 1003 , home private branch exchange 304 - i accordingly updates its table mapping off - premises telephone numbers to on - premises telephone numbers . fig1 depicts the transmission of signals among elements of telecommunications system 300 when affiliated wireless terminal 301 places a call , in accordance with the second illustrative embodiment of the present invention . in particular , fig1 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange 304 - i , and visitor private branch exchange 304 - j . it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig1 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig1 can be performed simultaneously or in a different order than that depicted . at signal transmission 1101 , affiliated wireless terminal 301 places a call by transmitting a signal to visitor private branch exchange 304 - j that specifies a particular destination ( e . g ., the telephone number of another wireless terminal , etc .) and instructs the pbx to route the call to the specified destination . at signal transmission 1102 , visitor private branch exchange 304 - j routes the call to server 310 , in well - known fashion . at signal transmission 1103 , server 310 routes the call to home private branch exchange 304 - i , in well - known fashion . at signal transmission 1104 , the portion of the call connecting visitor private branch exchange 304 - j to home private branch exchange 304 - i is dropped from the call , and that portion is replaced by a new least - cost call that does not necessarily pass through server 310 . the remaining portion of the original call is then connected with the new call , in well - known fashion . at signal transmission 1105 , the connected call is then extended to the specified destination , in well - known fashion . as will be appreciated by those skilled in the art , the call might be extended to a destination whose telephone number is in the address space of home private branch exchange 304 - i , or an extension within the address space of home private branch exchange 304 - i that does not correspond to any terminal , or might be routed externally to a terminal whose telephone number is outside the address space of home private branch exchange 304 - i ( as depicted in fig1 ). fig1 depicts the transmission of signals among elements of telecommunications system 300 when affiliated wireless terminal 301 receives a call that is directed to its associated on - premises terminal , in accordance with the second illustrative embodiment of the present invention . in particular , fig1 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange 304 - i , and visitor private branch exchange 304 - j . it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig1 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig1 can be performed simultaneously or in a different order than that depicted . at signal transmission 1201 , home private branch exchange 304 - i receives a call that is directed to the on - premises telephone number associated with affiliated wireless terminal 301 . as will be appreciated by those skilled in the art , the call might originate from a terminal whose telephone number is in the address space of home private branch exchange 304 - i , or might originate from a terminal whose telephone number is outside the address space of home private branch exchange 304 - i ( as depicted in fig1 ). at signal transmission 1202 , home private branch exchange 304 - i routes the call to server 310 , in well - known fashion . at signal transmission 1203 , server 310 routes the call to visitor private branch exchange 304 - j , in well - known fashion . 83 at signal transmission 1204 , the portion of the call connecting home private branch exchange 304 - i to visitor private branch exchange 304 - j is dropped from the call , and that portion is replaced by a new least - cost call that does not necessarily pass through server 310 . the remaining portion of the original call is then connected with the new call , in well - known fashion . at signal transmission 1205 , visitor private branch exchange 304 - j extends the call to affiliated wireless terminal 301 , in well - known fashion . fig1 depicts the transmission of signals among elements of telecommunications system 300 when affiliated wireless terminal 301 places a call , in accordance with the third illustrative embodiment of the present invention . in particular , fig1 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange 304 - i , and visitor private branch exchange 304 - j . it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig1 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig1 can be performed simultaneously or in a different order than that depicted . at signal transmission 1301 , affiliated wireless terminal 301 places a call by transmitting a signal to visitor private branch exchange 304 - j that specifies a particular destination ( e . g ., the telephone number of another wireless terminal , etc .) and instructs the pbx to route the call to the specified destination . at signal transmission 1302 , visitor private branch exchange 304 - j routes the call to server 310 , in well - known fashion . at signal transmission 1303 , server 310 routes the call to home private branch exchange 304 - i along a route that includes visitor private branch exchange 304 - j , in well - known fashion . at signal transmission 1304 , the portion of the call connecting visitor private branch exchange 304 - j to server 310 back to visitor private branch exchange 304 - j is dropped from the call . at signal transmission 1305 , the call is then extended to the specified destination , in well - known fashion . as will be appreciated by those skilled in the art , the call might be extended to a destination whose telephone number is in the address space of home private branch exchange 304 - i , or an extension within the address space of home private branch exchange 304 - i that does not correspond to any terminal , or might be routed externally to a terminal whose telephone number is outside the address space of home private branch exchange 304 - i ( as depicted in fig1 ). in some other embodiments of the present invention , signal transmission signal transmission 1304 might be omitted , and at signal transmission 1303 server 310 might instead establish a new call to home private branch exchange 304 - i along a route that includes visitor private branch exchange 304 - j . in such embodiments , the portions of the original and new calls connecting visitor private branch exchange 304 - j and server 310 are subsequently dropped , and the remaining portions of the original and new calls are then connected , in well - known fashion . in still some other embodiments , at signal transmission 1303 server 310 might transmit a signal that instructs visitor private branch exchange 304 - j to route the call to home private branch exchange 304 - i , in which case at signal transmission 1304 visitor private branch exchange 304 - j carries out this instruction . fig1 depicts the transmission of signals among elements of telecommunications system 300 when affiliated wireless terminal 301 receives a call that is directed to its associated on - premises terminal , in accordance with the third illustrative embodiment of the present invention . in particular , fig1 depicts the transmission of signals among affiliated wireless terminal 301 , server 310 , home private branch exchange 304 - i , and visitor private branch exchange 304 - j . it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention in accordance with fig1 ; moreover , it will be clear to those skilled in the art , after reading this disclosure , which signal transmissions of fig1 can be performed simultaneously or in a different order than that depicted . at signal transmission 1401 , home private branch exchange 304 - i receives a call that is directed to the on - premises telephone number associated with affiliated wireless terminal 301 . as will be appreciated by those skilled in the art , the call might originate from a terminal whose telephone number is in the address space of home private branch exchange 304 - i , or might originate from a terminal whose telephone number is outside the address space of home private branch exchange 304 - i ( as depicted in fig1 ). at signal transmission 1402 , home private branch exchange 304 - i routes the call to server 310 , in well - known fashion . at signal transmission 1403 , server 310 routes the call to home private branch exchange 304 - i along a route that includes visitor private branch exchange 304 - j , in well - known fashion . at signal transmission 1404 , the portion of the call connecting home private branch exchange 304 - i to server 310 back to home private branch exchange 304 - i is dropped from the call . at signal transmission 1405 , visitor private branch exchange 304 - j extends the call to affiliated wireless terminal 301 , in well - known fashion . in some other embodiments of the present invention , signal transmission signal transmission 1404 might be omitted , and at signal transmission 1403 server 310 might instead establish a new call to visitor private branch exchange 304 - j along a route that includes home private branch exchange 304 - i . in such embodiments , the portions of the original and new calls connecting home private branch exchange 304 - i and server 310 are subsequently dropped , and the remaining portions of the original and new calls are then connected , in well - known fashion . in still some other embodiments , at signal transmission 1403 server 310 might transmit a signal that instructs home private branch exchange 304 - i to route the call to visitor private branch exchange 304 - j , in which case at signal transmission 1404 home private branch exchange 304 - i carries out this instruction . as will be appreciated by those skilled in the art , although the illustrative embodiment is disclosed in the context of reducing toll charges , it will be clear to those skilled in the art , after reading this disclosure , how to make and use other embodiments of the present invention that reduce other kinds of costs ( e . g ., transmission delay , distance traveled , number of network segments traversed , etc .). as will be further appreciated by those skilled in the art , although the illustrative embodiment does not explicitly include any mechanism by which private branch exchanges 304 authenticate affiliated terminal 301 , such authentication methods are well - known in the art , and it will be clear to those skilled in the art , after reading this disclosure , how to make and use embodiments of the present invention that incorporate such methods . it is to be understood that the disclosure teaches just one example of the illustrative embodiment and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims .