in fig1 - 6 , which will be described hereinafter , applies generally that when a channel 1 , 4 , 5 , 6 , 11 , 12 , 13 , 21 , 31 passes through a telephone network n , the connection can either be established directly or via one or more exchanges or switching centres in the network n in a known manner . this is shown in broken lines . pure signalling channels 2 , 3 are shown in dotted lines . one possible way of conducting telefax detection when older telefax machines are used is to send a fictitious response with each telephony call , so that a possible telefax will begin to send its message . the receiving terminal then listens for any possible handshake signals or a possible telefax message and it is known after 3 - 4 seconds whether a telefax machine is calling or not . this procedure is satisfactory provided that it is actually a telefax machine that called . the problem is that all normal telephone calls will also be delayed by 3 - 4 seconds , which is unacceptable . the present invention utilizes , instead , the fact that it normally takes a few seconds before a person is able to answer the telephone . the use of intelligent network services also provides some control over the calling subscriber , because it is possible to some extent to control when a calling telefax machine shall send its telefax message and the like . fig1 and 8 illustrate detection of telefax messages in accordance with the invention . a subscriber calling from terminal a calls a special telephone number , block 102 . in the illustrated case , the calling terminal a may be a telephone or a telefax machine . a channel 1 is setup through the telephone network n to a service switching point ssp , in a known manner . the service switching point ssp is cognisant of the fact that the number called is a special type of telephone number and informs a service control point scp of the fact over a signalling channel 2 , this control point identifying the telephone number in turn , block 104 . in the illustrated case , the number is special inasmuch that the calling subscriber calls the same number from his calling terminal a irrespective of whether he wishes to call a telefax machine cf or a telephone ct . stored in the service control point scp are one or more telephone numbers for the called telephone ct on the one hand and for the called telefax machine cf on the other . a telephone answering machine may be used instead of the called telephone ct . switching is effected to that number which is activated at that moment in time . if there are several numbers to choose from , the concept is normally referred to as personal telephony or personal mobility ( upt , universal personal telecommunications ). subsequent to identifying the called number , the service control point scp signals the service switching point ssp over a signalling channel 3 and commands the service switching point to listen for a possible telefax message and to setup a channel 5 to a called telephone ct in accordance with relevant programming in the service control point scp , block 106 . the service switching point ssp sets up a channel 4 to a message centre mc and connects said channel with the channel 1 between the calling terminal a and the service switching point ssp . a fictitious response is then sent to the calling terminal a . if the calling terminal a is a telefax machine , it will now believe that the called telefax machine cf has answered and will begin to send a telefax message , optionally preceded by handshake signals . the service switching point ssp also sets up a channel 5 to the called telephone ct and a channel 6 to the message centre mc . these two channels 5 , 6 are then combined to provide a connection between the message centre mc and the called telephone ct via the service switching point ssp , whereafter the service switching point ssp orders the called telephone ct to begin to ring , block 108 . the message centre mc in turn is ordered by the service switching point ssp to lie and listen for a possible telefax message or possible handshake signals , block 112 , although for a pre - set maximum time , e . g . 3 - 4 seconds . the called telephone ct rings during this listening period . this procedure saves time ; it normally takes a few seconds for a person to answer the call . the message centre mc will normally have had time to detect the type of call concerned during this period . when the calling terminal a is , instead , a telephone , there will be no sound in the receiver during the 3 - 4 seconds during which detection takes place . normally , fictitious ringing signals are sent to the calling subscriber at the calling terminal a , so that the subscriber will &# 34 ; hear &# 34 ; the called telephone ct ringing on the other side . it is not appropriate , however , to send the signals whilst telefax detection is taking place , because this might possibly disturb any telefax machine that wishes to transmit . if telefax detection is found to be negative after 3 - 4 seconds and there is still no reply from the called telephone ct , the fictitious ringing signals are re - transmitted until someone answers the called telephone ct . a number of different alternatives can now occur , these alternatives being described one by one hereinafter . see fig2 a , 2b , 2c , 7 , 8 , 9a , 9b , 9c . if the message centre mc detects an incoming telefax message within 3 - 4 seconds , blocks 114 , 118 , the service switching point ssp will order the called telephone ct to stop ringing and releases the channel / channels 5 , 6 from the message centre mc to the called telephone ct , block 124 . during this time , the telefax message is received in the message centre mc and stored therein , block 142 . billing of the calling subscriber commences at the beginning of the transmission of the telefax message from the calling terminal a . according to one embodiment ( see fig1 a and 9a ), the whole of the telefax message is received initially in the message centre mc , block 142 . a channel 11 is then setup between the message centre mc and the called telefax machine cf , and the telefax message is then transmitted , block 144 . according to another embodiment ( see fig2 a and 9b ), a channel 11 is setup immediately between the message centre mc and the called telefax machine cf , blocks 142 , 146 . when the message centre mc has received a part of the telefax message , this message part is sent to the called telefax machine cf while the message centre mc continues to receive a further part of the telefax message . although time is saved in this way , a more intelligent message centre mc will , of course , be required . it is also conceivable not to use any form of intermediate storage and / or to setup a channel between the calling terminal a and the called telefax machine ct externally of the message centre mc . according to other embodiments shown in fig2 b , 2c and 9c , the telefax message remains in the message centre mc until someone calls from a telephone ct , block 148 , either to the service switching point ssp over a channel 13 , or directly to the message centre mc over a channel 12 and requests printing - out of the telefax message . the telefax machine cf on which the telefax message shall be printed - out may also be chosen as an optional feature . a channel 11 is then setup between the message centre mc and the called telefax machine cf , whereafter the telefax message is sent , block 150 . messages concerning the receipt of a telefax message may be transmitted as sms messages ( short message service ) or the like to a mobile telephone ct , thereby enabling the message characters to be sent to the mobile telephone ct and there displayed . alternatively , the subscriber must call at regular intervals on telephone ct and check whether or not a telefax message is waiting . finally , it is conceivable not to release the channel / channels 5 , 6 between the message centre mc and the called telephone ct when identifying a telefax machine as the caller , but to allow the called telephone ct to ring until someone answers . when the call is answered , a message to the effect that &# 34 ; you have received a telefax message . where do you wish it to be sent ?&# 34 ; is delivered . see fig3 and 8 . if , in the above example , the called telephone ct is answered before telefax detection is completed , block 114 , the message centre mc delivers to the called telephone ct a recorded message on the channel / channels 5 , 6 . the message may read , for instance , &# 34 ; facsimile detection is in progress . please wait .&# 34 ;, block 116 . if it is then found that the call actually was a telefax message , blocks 114 , 118 , 120 , the message centre mc delivers a further message , e . g . &# 34 ; you will receive a telefax message . please replace the receiver &# 34 ;, block 122 . when the telefax message is stored solely in the message centre mc , the alternative message &# 34 ; you have received a telefax message . where do you want it sent ?&# 34 ; may be delivered . if the message centre mc does not detect any incoming telefax messages , the channels 4 , 6 between the service switching point ssp and the message centre mc are released ; see fig4 and 8 , block 118 . instead , the service switching point ssp connects the channel 5 between the terminal a and the service switching point ssp with the channel 1 between the service switching point and the called telephone ct , block 130 . when the receiver of the called telephone ct is then lifted , block 132 , fig1 abc , the call can be dealt with in a conventional manner , block 136 . should the called telephone ct of the above example be answered before telefax detection is completed , block 114 , the message centre mc will deliver a recorded message to the called telephone ct , along the channel / channels 5 , 6 ; see fig5 and 7 . the message may be to the effect that &# 34 ; telefax detection is in progress . please wait .&# 34 ;, block 116 . if it is later found that the call did not relate to a telefax message , blocks 114 , 118 , 126 , the message centre mc sends another message , e . g . &# 34 ; call established &# 34 ;, block 134 , so that the person who answered the telephone will be aware that the telefax detection process has been completed and that it was a person who called and not a telefax machine , block 136 . see fig4 and 6 . if the message centre mc does not detect an incoming telefax message , block 118 , the channels 4 , 6 between the service switching point and the message centre mc are released , block 130 . the service switching point ssp instead connects the channel 1 between the calling terminal a and the service switching point ssp to the channel 5 between the service switching point ssp and the called telephone ct . if the receiver of the called telephone ct has still not been lifted after a given time lapse , a new channel 21 is setup between the message centre mc ( or some other message centre mc ) and the service switching point ssp . this channel 21 is coupled to the channel 1 between the service switching point ssp and the calling terminal a . the message centre mc then sends to the calling terminal a on the channel / channels 1 , 21 a message , that may read , for instance , &# 34 ; still searching for the subscriber . please wait .&# 34 ;, fig1 b , block 162 . one or more connections to other telephones ct can then be tested , block 164 , or a connection to a telephone answering machine may be made , fig1 c , blocks 166 , 168 . as illustrated in fig1 a , an alternative is simply to allow the called telephone ct to ring until someone answers or until the subscriber of the calling terminal a gives up and replaces the telephone receiver , blocks 132 and 160 . only telefax machines and messages have been dealt with in the aforedescribed embodiments . it will be understood that other forms of data transmissions over a telephone network can be carried out in an equivalent manner , e . g . between computers provided that the computers understand one another . it is also , of course , conceivable to listen for several types of data simultaneously and to forward the data to the correct location , depending on type . accordingly , the service switching points ssp , the service control points scp and the message centres mc have been drawn inside the telephone network n , although it will be understood that the same function can be achieved in a similar manner outside the telephone network n . the service control point scp may also be integrated with the service switching point ssp in one and the same point or node . the messages delivered by the message centre may also be presented in a way other than by voice , for instance presented on a telephone display . when reference is made in the description to the action of &# 34 ; lifting a receiver &# 34 ;, it will be understood that mobile telephones , loudspeaker telephones and the like with which a receiver is not lifted in order to answer a call are also included .