Abstract: A method of processing data for paying for at least one of item in a system having a Payment Gateway server and a mobile device is disclosed. The method includes steps of downloading an application by using address information in a memory of the mobile device, transmitting user information stored in the USIM of the mobile device to the PG server if the first phone number is identical with the second phone number, generating ID information for the user in the PG server, transmitting first barcode from the PG server to the mobile device if the mobile device requests a barcode to the PG server, transmitting request signal for second barcode from the mobile device to the PG server if a specific item is selected by the user of the mobile device, and transmitting the second barcode from the PG server to the mobile device.