Intercom Call : 【*0】
The intercom feature allows you to dial a phone and have the phone automatically go off-hook to speakerphone mode. This is useful for announcing callers or paging individuals who may not be near their phone.
To make an intercom call, dial the intercom access code (usually *0) followed by the extension number of the party you wish to intercom.
Note that intercom is a phone-specific feature. Most phones support intercom but some do not. The feature can also be disabled on most phones directly.