Abstract: An improved key telephone system realizes substantial reduction in installation costs, permits use of relatively small central units, provides compatability with telephone apparatus speaker phones, automatic dialers, etc., and provides additional advantages.

Abstract: A telephone system comprises a plurality of station sets, each including a plurality of key buttons, and the system includesA. a station circuit for at least one of the station sets, said station circuit including interface means for transferring data to and receiving data from its associated station set, said interface means including between 2 and 3 pairs of wires connected with the station set, one pair of which is a talk pair, and the remainder of which is or are for power transmission and for transmission of data related to line, status and audible signalling and for control information including switch status, andB. a line circuit for at least one line, each line circuit including means for transmitting control, status and talk information to, and receiving control, status and talk information from, at least one station circuit connected therewith.