Method and apparatus for providing outside network service based on advertisement viewing

PURPOSE: A method for providing an advertisement based external network service and a device thereof are provided to offer telephony service for free through a mobile device in public place, thereby increasing the advertisement effect. CONSTITUTION: A mobile gateway(200) allocates an IP address to a mobile device(300). The mobile gateway receives an external network service request message from the mobile device. When the mobile device does not have an access right to the external network, the mobile gateway transmits an advertisement to the mobile device. The mobile gateway gives the access right to the mobile device when receiving an advertisement viewing report message.