Abstract: A method and apparatus in which (i) a user equipment device registers with a first radio access network (RAN) that provides connectivity with a transport network, (ii) once registered with the first RAN, the device then registers via the first RAN and transport network with a call server, and (iii) in response to the device registering with the call server, but before the device then engages in a call served by the call server, the device registers via the first RAN with a second RAN. The method may thereby help to expedite later handover of a call served by the call server from being via the first RAN to being via the second RAN. Further, by the second RAN registration being conducted in response to registration of the device with the call server, the method may help to ensure usefulness of the registration of the device with the second RAN.