CALLOUT SIGNAL SYSTEM FOR DOOR PHONE

PURPOSE:To recognize a visitor during the call between extensions, by preventing a callout tone of high level from being mixed to the extension calls through the stopping of the display for callout ringing of a telephone set, when a callout comes from a door phone while a button telephone set is in service. CONSTITUTION:A main device ME is connected to a button telephone set TEL, a microprocessor CPM of the ME and an extension circuit PRV are connected to a door unit DHU and a door phone DH is connected to the unit DHU. An extension call display lamp PL, a door phone call display lamp DL, and a speaker SPT connected to an amplifier AMT are connected to a microprocessor CPT of the telephone set TEL. When the telephone set TEL is busy, if a call comes from a door phone DH, the display of a display lamp PL is stopped with the processor CPM and CPT, the extension circuit PRV changes over a switching circuit ECX to prevent a channel network NWT for telephone set from being mixed with a call tone of high level.