Patent ID: 7096020

Claim:
A method of implementing a handoff using a multiparty (MPTY) service from a first base station (BS) that provides a communication service in a first communication scheme to a second BS that provides a communication service in a second communication scheme different from the first communication scheme in a mobile communication system, the method comprising the steps of: upon sensing a handoff to the second BS, asking a visitor location register (VLR) connected to the second BS for an availability of an MPTY call through a home location register (HLR) connected to the first BS by a mobile station (MS); notifying the MS of the availability of the MPTY call through the HLR if the MPTY call is available, and ordering a mobile switching center (MSC) that is connected to the VLR to activate the MPTY call by the VLR; requesting the MSC to maintain one of active MPTY calls by the MS when the MS senses the availability of the MPTY call and transitions to a second state; maintaining the active MPTY call to be assigned to the MS by the MSC; and establishing a call in the second communication scheme using the maintained MPTY call through the HLR when the MS transitions to a third state and ending a call in the first communication scheme by the MS.