Patent ID: 8862164

Claim:
A method comprising: receiving, by a network transition gateway controlled by a mobile virtual network operator (MVNO), a first message directly from a mobile device indicating that the mobile device is in a session initiation protocol (SIP) wireless hotspot, wherein the first message is received directly from the mobile device by the network transition gateway and does not pass through a cellular network, and wherein the mobile device is present in a session initiation protocol (SIP) home location register (HLR) of the network transition gateway that lists mobile devices belonging to customers of the MVNO; receiving, by the network transition gateway, a second message directly from the mobile device indicating that the mobile device is engaged in a communication session with a second device using a first call leg via the cellular network while in the SIP wireless hotspot, wherein the second message is received directly from the mobile device by the network transition gateway and does not pass through the cellular network, and wherein the MVNO and the network transition gateway have no control over the cellular network and wherein the network transition gateway is configured to send only requests for establishing, routing, and breaking down a call to the cellular network; requesting, by the network transition gateway, that a public switched telephone network (PSTN) gateway add the mobile device to the communication session using a second call leg via the SIP wireless hotspot and terminate the first call leg, wherein the PSTN gateway is separate from the cellular network and is not controlled by the MVNO; receiving, by the network transition gateway, an affirmative response from the PSTN gateway; and sending, by the network transition gateway, a third message to the mobile device to notify the mobile device of the affirmative response.