Patent ID: 7269655

Claim:
A method for providing an instant messaging service in a Session Initiation Protocol (SIP) server of a mobile communication system, said system including the mobile terminals, an instant messaging service (IM) server and the SIP server, the method comprising the steps of: receiving a Session Initiation Protocol (SIP) message according to a requesting type for an instant messaging service from a mobile terminal, wherein the Session Initiation Protocol (SIP) message includes a message-body including at least one of a FUNCTION field indicating a function of the SIP message, an action (ACT) field indicating an operation of the indicated function, a category (CAT) field indicating a range in which the indicated operation is performed, a user identification (UID) field indicating a sender of the SIP message, a target user identification (TID) field indicating a target user for the indicated operation, a DATA field containing data according to the indicated function, and a RESULT field containing a result of a request; and transmitting the Session Initiation Protocol (SIP) message to the IM server.