Methods and systems for providing a mobile office phone are provided herein. In one embodiment a system includes a private branch exchange (PBX), a server configured to integrate user equipment (UE) onto the PBX by attaching a mobile telephone number of the UE as an extension on the PBX, and a session initiation protocol (SIP) server coupled with the server and PBX that allows the UE to place and receive calls and messages over data channels of a network.