Patent ID: 8611893

Claim:
A method for roaming between networks, comprising: subscribing to a presence server to determine a presence of a mobile unit, the presence server comprising a service that generates a notification of the presence of the mobile unit; receiving the notification of the presence of the mobile unit from the presence server; creating a state reflecting the presence of the mobile unit at a Signal Transfer Point (STP) that is co-located on a boundary of a first network and a second network; routing a call through the STP that is co-located on the boundary of the first network and the second network whether the call is established within the first network or the second network, wherein the STP uses the state to determine over which network to route the call; determining that the presence of the mobile unit changes from the first network to the second network; offloading signaling of the call through the STP to the second network; and retaining connection information associated with the first network at the SIP to facilitate reconnection with the first network.