A mobile client can include a first voice interface to communicate over a first network and a second voice interface to communicate over a second network. The mobile client includes a data interface to perform signaling with a private branch exchange (PBX) of an enterprise system and a call control. The call control can determine that an established media session between the mobile client and a third party requires a handoff from the first network to the second network and signal the PBX to establish parameters for the handoff via the data interface. The call control can also perform the handoff of the established media session between the mobile client and the third party to the second network according to the parameters.