According to one aspect, a system and method of exchanging GRUUs (Globally Routed User Agent URI (Uniform Resource Identifier)) between a first telephony-enabled device and a second telephony enabled device using a circuit-switched message is provided. Once exchanged, the telephony enabled devices can exchange SIP (session initiated protocol) communications routed by the GRUUs. Any one of the telephony-enabled devices can add a media component to the SIP communications. According to another aspect, a system and method of generating GRUUs is provided. According to another aspect, a system and method of handing off communications to a packet switched network from a circuit switched network is provided.

According to one aspect, a system and method of exchanging GRUUs (Globally Routed User Agent URI (Uniform Resource Identifier)) between a first telephony-enabled device and a second telephony enabled device using a circuit-switched message is provided. Once exchanged, the telephony enabled devices can exchange SIP (session initiated protocol) communications routed by the GRUUs. Any one of the telephony-enabled devices can add a media component to the SIP communications. According to another aspect, a system and method of generating GRUUs is provided. According to another aspect, a system and method of handing off communications to a packet switched network from a circuit switched network is provided.

The invention includes a method of providing media data of a SIP-based Auxiliary Service from an Auxiliary Application Server, AS, to a recipient peer of an established communication exchange between peers. The method includes issuing an invocation to the Auxiliary AS, the invocation including an indication of the recipient peer of the Auxiliary Service. The Auxiliary Service media data is prepared and sent to the recipient together with a correlation ID identifying the established communication exchange, and an Application Classmark identifying the auxiliary service.

A SIP ancillary data server provides host to auxiliary data for an emergency SIP session (call) uniquely referred to in a transported SIP header. In a manner similar to how location is represented in an emergency call, a SIP header is extended. The extended SIP Header contains one of two possible types of content elements: either (a) a content pointer element to a SIP Message body part (a cid:, or content identifier); or (b) an <information_URI> (a.k.a, info_URI in this document).