Registration with radio access network in response to registration with call server

A method comprising:

• registering, by a user equipment device (UE), with a first radio access network (RAN);
• once the UE is thereby registered with the first RAN, registering by the UE, via the first RAN, with a call server that is configured to serve calls, wherein the call server is a voice over Internet Protocol (VoIP) call server, and wherein the registering by the UE with the call server establishes a registration of the UE with the call server;
• in response to the UE registering with the call server, but before the UE engages in any calls served by the call server based on the registration with the call server, registering by the UE, via the first RAN, with a second RAN, wherein the registering by the UE with the second RAN establishes a registration of the UE with the second RAN;
• once the UE is thereby registered with the first RAN, with the call server, and with the second RAN, the UE beginning to engage via the first RAN in a call served by the call server;
• and
• while engaged in the call, handing over by the UE from engaging in the call via the first RAN to engaging in the call via the second RAN, wherein the handing over to engaging in the call via the second RAN is based on the earlier registration of the UE with the second RAN, thereby avoiding a need for the UE to register with the second RAN when engaging in the handing over.

A device comprising:

• a wireless communication interface;
• and
• a controller configured to (i) register the device, via a first radio access network (RAN) serving the device, with a call server and (ii) in response to registering the device with the call server, but before the device then engages in any calls served by the call server, register the device, via the first RAN, with a second RAN,
• wherein the call server is a voice over Internet Protocol (VoIP) call server,
• wherein registering the device with the call server comprises transmitting via the wireless communication interface to the call server a registration request message and receiving via the wireless communication interface from the call server, in response to the registration request message, a registration response message indicating successful registration of the device with the call server, and
• wherein registering the device with the second RAN in response to registering the device with the call server comprises registering by the device with the second RAN in response to the indicating of successful registration of the device with the call server.