A private branch exchange (PBX) mobility system and associated method for re-using of call legs in an enterprise system. The enterprise system includes a session management platform (SMP) having a private branch exchange (PBX) mobility enabler, the PBX mobility enabler having third-party control communications to one or more PBXs over a session control interface, such as a Session Initiation Protocol (SIP) interface. The PBXs are in communication with one or more media servers. The PBX mobility enabler is configured to provide control communications to the PBXs over the session control interfaces to re-use a wireless call leg and connect to other call legs.