A telephone which can receive and transmit voice and asynchronous data simultaneously is provided. A signalling circuit provides signals indicating the request for a communication link or requesting a communication link to a predetermined location. A transceiver circuit synchronously receives and transmits frames of digital data bits representing data, voice and signalling information. A voice digitizer circuit converts the received frames of digital bits to an analog output and converts a received voice signal to a digital voice output. An interface circuit is used to interface between an asynchronous data source and the synchronous transceiver circuit. The telephone is line powered by utilizing D.C. isolating transformers to power both voice and data circuitry.