Abstract: An intercom calling apparatus in a key telephone system including a page switch for switching the transmitter from a talking circuit network to an intercom calling path while a contemporaneous call on a central office line is held by the series combination of a resister and a varistor forming a parallel circuit with the transmitter in the talking circuit network.

Abstract: In a communication system of a key telephone system wherein a key telephone selected by electric power supplied from a key service unit is started through a signal line for performing an independent calling, the key service unit is provided with a voice switch adapted to switch between transmission and reception of speech, each key telephone is provided with answer signal sending means including a microphone, and a common line is connected to the outputs of the answer signal sending means of respective key telephones for sending the outputs to the voice switch, thus permitting a selected key telephone to perform a hand-free communication.