Abstract: A telephone-stereo "speakerphone" telephone amplifier apparatus is disclosed, the apparatus comprises a standard telephone, a home entertainment variety stereo amplifier, two loudspeakers and microphone mixer (including signal sources) connected by an interface coupler which serves as a junction location for routing of interconnecting wires and a housing for a mode switch and protective circuitry, transforming the component parts into a full duplex (simultaneous two way) transmit preamplifier and receive monitor audio communication system. To enhance convenience the interface coupler provides a mode switch for selection of one of two desired modes of operation. In one position (telephone interface mode) the switch automatically makes all necessary connections for operation of the components in combination as a telephone-stereo "speakerphone" telephone amplifier. In the other position (stereo mode) the switch breaks contact between the telephone and stereo and returns both to independent normal operation.