Call from switchboard 1
For incoming intercom calls, it is not possible to mute the ringer before a call is received. It is only possible to
mute the ringer for the current call. Once muted, the ringer cannot be switched back on during the current call,
so the icon disappears.
The call is answered using the P/A key, after which the situation is the same as with an outgoing call.
The conversation can be ended using the P/A key or by the calling internal unit using the appropriate procedure.