Efficient selection of interoperability gateway for CDMA terminated PTT calls

In a communications system including a first Push-to-Talk (PTT) network, and a second PTT network having a plurality of interoperability gateways, a method for efficiently selecting an interoperability gateway for PTT calls terminated at the second PTT network comprising:

• receiving, by a PTT interoperability infrastructure, a PTT call request from the first PTT network, the PTT call request identifying a target subscriber unit on the second PTT network;
• forwarding, by the PTT interoperability infrastructure, the PTT call request to a first interoperability gateway of the second PTT network;
• receiving, by the PTT interoperability infrastructure, a notification that the PTT call request has succeeded, the notification including an identification of the target subscriber unit and an identification of a second interoperability gateway of the second PTT network, wherein the second interoperability gateway corresponds to a current location of the target subscriber unit;
• storing, by the PTT interoperability infrastructure, an identifier of the target subscriber and an identifier of the second interoperability gateway in a cache for subsequent use in routing calls to the target subscriber unit;
• and
• routing a subsequent PTT call request from the first PTT network identifying the target subscriber unit to the second interoperability gateway of the second PTT network.