Key telephone systems

摘要

A key telephone system adapted to selectively connect a plurality of key telephone sets to a plurality of CO lines through a key service unit and pluralities of talking lines and control lines and provided with a calling device in at least one of the key telephone sets, in which automatic holding of the CO line is enabled upon depression of a calling key. In case of transferring the incoming call from a receiving key telephone set to a called one of the other key telephone set, depression of the individual calling switch automatically starts calling of the called key telephone set and enables the called party to recognize the incoming call by means of lamp indication and answer the calling CO line. The number of cable conductors interconnecting the key service unit and the key telephone sets is effectively reduced.