1. A method for operating a terminal in a mobile communication system, the method comprising: receiving a signal; determining whether the received signal corresponds to a session initiation protocol (SIP) update request message; if the received signal corresponds to an SIP update request message, sending the SIP update request message to an SIP processor in a communication processor without sending the SIP update request message to an application processor; and handling the SIP update request message by the SIP processor, wherein the application processor is in sleep mode if the received signal corresponds to the SIP update request message.