In those instances wherein inter-exchange handoff of a cellular call occurs, and a mobile station desires to activate an in-call service change with respect to that cellular call among and between a plurality of supported voice and data services, a change of service request message is initiated by a...http://www.google.fr/patents/US6125276?utm_source=gb-gplus-shareBrevet US6125276 - Inter-exchange signaling for in-call service change requests
Inter-exchange signaling for in-call service change requests
