User equipment, mobile communication system and method

A mobile communication system, comprising:

• user equipment supporting an IMS function;
• and
• a network wirelessly connected to the user equipment,
• wherein the user equipment includes:
• an application layer configured to provide a user interface for a user to set ON or OFF the IMS function;
• a SIP layer configured to enable or disable transmission of a SIP signal to a resident network corresponding to user's setting ON or OFF the IMS function in the user interface;
• and
• a modem layer configured to change an IMS related Capability of the user equipment related to the IMS function corresponding to user's setting ON or OFF the IMS function in the user interface and communicate with the resident network based on the changed Capability.

A method for setting an IMS function in user equipment, the method comprising:

• providing a user interface for a user to set ON or OFF the IMS function;
• receiving user's setting ON or OFF the IMS function in the user interface;
• enabling or disabling transmission of a SIP signal to a resident network corresponding to the received setting ON or OFF the IMS function;
• changing an IMS related Capability of the user equipment related to the IMS function corresponding to the received setting ON or OFF the IMS function;
• and
• communicating with the resident network based on the changed Capability.