A method of roaming between a cellular network and a wireless network can include receiving an invitation over the wireless network. The invitation can be sent from a mobile communications device engaged in a cellular call over a cellular voice channel. The method also can include authenticating the mobile communications device over the wireless network, sending an acknowledgement of the invitation to the mobile communications device over the wireless network, and initiating a handoff. The established cellular call can be switched from the cellular network to the wireless network.