an internal telephone intercom system including means for connecting to a dedicated telephone communication line , a plurality of telephone sets connected to the line and adapted for telephone communications with locations external to said dedicated line , an audio receiving means at each telephone set for receiving audio signals from a microphone within said telephone set , a radio frequency generator means for generating a carrier frequency and amplitude modulated responsive to said audio signals with said modulated signal being multiplexed on said dedicated line , an audio expander for receiving a modulated signal from the radio frequency generator means and producing an audio signal responsive to audio sounds at a speaker .