Exchange and use of globally unique device identifiers for circuit-switched and packet switched integration

A mobile device for handing off a circuit switched (CS) communication with a second mobile device from a CS network to a packet switched (PS) network, the mobile device comprising a wireless radio, the mobile device being configured to:

• determine that the mobile device should attempt to handoff the CS communication to the PS network;
• send, by the wireless radio, a first identity wherein the first identity is sent in an information element of a cellular protocol message;
• send, by the wireless radio, a Session Initiation Protocol (SIP) message for a PS communication, the SIP message including a second identity in a format of a Unified Resource Name (URN) in an instance identifier (ID) contained within the SIP message, wherein the CS communication and the PS communication originate from the mobile device when the first identity matches the second identity;
• continue the PS communication with the second mobile device via the PS network;
• and
• drop the CS communication with the second mobile device.