Let me explain my problem:
The call comes in my SIP TRUNK;
Extension 21 picks up the call;
Extension 21 do an attended transfer do ext 31;
Ext 31 talking to the caller;
… then ext 21 rings… when picked up, the ext 21 is joined into the conversation between ext 31 and the external caller.
Seems to me like a ‘automatic conference’ starded somewhere or for someone.
The phones are GXP1610, 1615 and 1630.