Abstract: A key telephone system has output circuits connectable to a plurality of outside lines which are connected to a central exchange. A wireless telephone having a base unit with first and second output terminals and a separable cooperating handset unit having a manually operable number entry device is associated with the system. These units have cooperating radio transmitters and receivers which permit wireless communication links to be established between the units. A cordless telephone - key telephone interconnection interface has first and second output terminals respectively connected to the first and second output terminals of the base unit and output terminals connected to the output circuits of the key system. The interface establishes a plurality of calling numbers for the outside lines to be employed by a user of the handset unit.