An instant log-in method for authentificating a user and settling bills by using two different communication channels and a system thereof

PURPOSE: A method and system for authentication and payment instant log-in user using different communication network are provided, which dose not need a user register procedure by using one user ID which is a terminal address or number of the second communication network such as a wire telephone network or wireless network in authorizing a user. CONSTITUTION: A user accesses a system of a service provider(200). The service provider transmits a service access screen to the user's computer according to the user's access request(205) and displays a screen accessing the user's web browser(210). The user inputs and transmits the terminal number of the second communication network to the service provider(215). The service provider generates the user's ID code(220). The service provider transmits the user's ID code to the user's second terminal(225) and displays a predetermined message on the second terminal(230). The user transmits a user confirmation response to the service provider(235,240). The service provider confirms the user' ID code included in the user confirmation response(245). The user generates a user authentication code(260). The user transmits and receives the user authentication code to and from the service provider and uses a service(265,270).