A mobile device registers with an infrastructure device coupled to a first communication network and then sends a request to activate PTT service in the first communication network. A communication server is adapted to receive the request to activate the PTT service, and to, thereby, activate the PTT service for the mobile device in the first communication network. Responsive to receiving the request to activate the PTT service, the communication server makes a determination to register the mobile device with a second communication network, generates a service registration message, on behalf of the mobile device, to register the mobile device with the second communication network, and sends the service registration message to the second communication network.