voice transmission unit 106 in the setup and clear down of a voice connection signaling data for the setup or respectively clear down of the voice connection are sent to the other side on the line 22 according to itu standard h 225 and h 245 there are control lines 107 a and 107 b between the signaling and transmission unit 100 and the voice transmission unit 106 via the control line 107 a the voice transmission unit 106 is informed that a voice connection exists between terminal equipment 10 and line trunk group 16 moreover which numbers the data packets with the voice data should have for identifying the connection is signaled to the voice transmission unit 106 further messages for signaling on the control line 107 a derive from the itu t standard h 323 the messages transmitted on the control line 107 b also derive from standard h 323 a user interface 108 of the terminal equipment 10 contains programs which when processed allow additional supplementary service in the terminal equipment 10 to be used the user interface 108 is connected to the signaling and transmission unit 100 or respectively to the voice transmission unit 106 via bidirectional control lines 109 a or respectively 109 b with the assistance of the user interface 108 operating elements with which the additional supplementary service.