A telecommunications system is disclosed that enables a user to pair a desk set that is an extension of a private-branch exchange with a cell phone that is accessible via the Public Switched Telephone Network. One feature of the telecommunications system enables an active call that is between the desk set and another party, to be transferred to the user's cell phone, while in the presence of third-party call control. This is advantageous because a user who is initially on a call at her desk set, but needs to get somewhere else (e.g., a meeting, the airport, home, etc.), is able to continue the call by transferring it to her cell phone. The third-party call control can be part of a computer-telephony integration (CTI) application—for example, in a telephone telemarketing center, which concurrently handles many active telephone calls.