Abstract: A telephone conversion device for converting a multiple line electromechanical telephone system having an electromechanical key system unit (KSU) for use with electronic telephones. Each conversion device includes a wall unit having a 50-pin connector for mating with the 50-pin connector of the KSU outlet cable, and a keystrip unit positionable on the desk of the user and upon which an electronic telephone is positioned. A slender 8-wire cord extends between the keystrip and wall units. The wall unit includes a first microprocessor which operates with a line status detector for determining the operational status of five multiple telephone lines by sensing the lamp driving signals provided by the KSU. Relays under the operation of the first microprocessor connect a selected line to a common talking pair which extends within the cord between the units for connection to the telephone. A detector detects when the receiver is off-hook.