Within a mobile communications device, a method of roaming between a mobile network and a wireless network can include establishing a Voice-Over Internet Protocol communications link with an endpoint over which a call is conducted, wherein at least a portion of the call is conducted over the wireless network. The method further can include initiating a handoff of at least a portion of the call from the wireless network to the mobile network using a Session Initiation Protocol refer method and continuing the call using the mobile network for at least a portion of the call rather than the wireless network.