Call Hold not invoked by buttons
Pressing a call holding button or a call transfering button does not invoke the Call Hold state.
In order to transfer a call, the SIP client, you use, must have a transfer button which sends REFER or DTMF. (Customized for Brekeke PBX)
To the phone, which has its own transfer button under specification of other IP, PBX may not allow you to forward calls.