Abstract: A modem located on a PC card. An I/O socket is mounted on one end of the PC card and sideswipe contacts are positioned long e one or more sides. The I/O socket has a plurality of positions including one or more positions which are electrically connected to the modem. A relay is located in the PC card, and has one side connected in common to the modem and the positions on the I/O socket. The other side of the relay is connected to the sideswipe connectors. The control input to the relay is connected to a position of the I/O socket separate from the modem positions. A voltage source is connected to a position in the socket separate from the modem positions and the control signal position. An I/O plug is designed to have one side connected to the telephone network and the other side connected to the I/O socket such that all pins in the plug mate with the corresponding positions in the I/O socket.