Terminal, method and system for performing combination service using terminal capability version

A method for providing a circuit switched (CS) service, a session initiation protocol (SIP)-based service, or a CSI service which is a combination of the CS service and an Internet Protocol (IP) multimedia subsystem (IMS) service, the method comprising:

• receiving, by a terminal, a terminal capability version of at least one target terminal;
• comparing, by the terminal, the received terminal capability version with a previously stored terminal capability version of the at least one target terminal;
• and
• sending a message for requesting for terminal capability information of the at least one target terminal from the at least one target terminal, if the received terminal capability version of the at least one target terminal is different from the previously stored terminal capability version of the at least one target terminal based on the comparison result,
• wherein if the received terminal capability version of the at least one target terminal is the same as the previously stored terminal capability version of the at least one target terminal, then the method proceeds with a CS or IMS process,
• wherein the terminal capability version identifies a version of capabilities of the at least one target terminal,
• wherein the terminal capability version is updated when the terminal capability information is changed, and
• wherein the terminal capability information includes at least one of:
• supported media format parameters,
• a Mobile Station International Subscriber Directory Number (MSISDN),
• a preferred Session Initiation Protocol (SIP) Uniform Resource Identifier (URI), or
• a supported Multimedia Message service (MMS) version.