A gateway for routing an international mobile telephone call comprises a storage device and a cost-saving routing module. The storage device is configured to store a mapping table and a call record table. The mapping table records a mobile phone number of a roaming subscriber and a fixed network number, and the call record table records a caller's phone number and the mobile phone number of the roaming subscriber. The cost-saving routing module is configured to establish a connection in accordance with the mapping table and call record table.