Only UC suite will log off your desk phone, all other options, such as ST500 (my preferred option), Xlight , 3CX etc. will require a forced log off (Cmd 90-23) and may well need additional programming to reinstate it. I usually recommend biting the bullet and buying additional VoIP extension/port licencing and create additional extensions that are then forwarded to set to ring both. Also set the twinned extension to send the CLI of the extension it is twinned with!