Mobile Twinning allows a user to twin their office desktop phone with an external device such as their mobile / cell phone. IP Office will pass on the original Caller ID so that the user can respond accordingly the user cannot access IP Office features on the mobile / external phone when answering a twinned call. However if the user picked up the call on the external device or cell phone, he / she could walk to his / her desk and pick up the twinned call by pressing a key on the office digital / IP phone or entering a short-code on the office analog phone.