an apparatus for providing an intercom function on a telephone , without the need for an external power supply , having dtmf or pulse capabilities including an intercom operation device arranged for connection to a dtmf or pulse telephone line and to a dtmf or pulse telephone instrument . the apparatus includes a device for sensing an extension selection dual input from the dtmf or pulse telephone instrument and transmitting a corresponding extension address signal over the dtmf or pulse telephone line . also included is an apparatus for sensing a received extension address signal from the telephone line , determining whether it corresponds to the telephone instrument to which the intercom operation apparatus is connected and , upon determination of correspondence , providing an extension selection ring output .