Abstract: The present invention relates to an interface apparatus between a digital computer and an analog communication medium. The interface apparatus has a telephony apparatus for transmitting or receiving the voice signals and a modem for transmitting or receiving the data signals. A switch is interposed between the telephone line and the modem and the telephony apparatus. The switch can be alternatively switched such that the telephony apparatus is connected to the telephone lines and transmits and receives voice signals and the modem is connected to receive data carrier signals that precede digital data signals and follow the digital data signals to and from the medium, or in the second position wherein the modem is connected to transmit and to receive digital data signals. The interface apparatus further has an interrupt for interrupting the operation of the computer and for causing the computer to be in communication with the modem and for switching the switch to connect the modem with the medium.