A system for providing a united messaging service, the system comprising: a service client configured to register membership registration information of a subscribed user and to provide a function of setting a service type to a subscribed user through a website; a database, DB, configured to store membership data of the subscribed user including membership registration information of the subscribed user, the service type of the subscribed user, and identification information related to an address of the subscribed user; a server configured to receive the membership data from the database and to provide the membership data in response to a query; and an SMS/MMS gateway configured to receive a short message service message or a multi-media service message transmitted from a SMS/MMS transmitting terminal through a message gateway, and to convert the message into a format determined by the service type; wherein the SMS/MMS gateway is also configured to extract a telephone number of the called party from the received message and query the extracted telephone number of the called party with the server to receive the ID information and the service type related to the extracted telephone number of the called party; wherein the short message service message or the multi-media service message is transmitted through the message gateway according to the telephone number if a telephone corresponding to the telephone number is capable of transmitting/receiving the short message service message or the multi-media service message, otherwise the converted message is transmitted through the SMS/MMS gateway to the called party according to the ID information. a service client configured to register membership registration information of a subscribed user and to provide a function of setting a service type to a subscribed user through a website; a database, DB, configured to store membership data of the subscribed user including membership registration information of the subscribed user, the service type of the subscribed user, and identification information related to an address of the subscribed user; a server configured to receive the membership data from the database and to provide the membership data in response to a query; and an SMS/MMS gateway configured to receive a short message service message or a multi-media service message transmitted from a SMS/MMS transmitting terminal through a message gateway, and to convert the message into a format determined by the service type; wherein the SMS/MMS gateway is also configured to extract a telephone number of the called party from the received message and query the extracted telephone number of the called party with the server to receive the ID information and the service type related to the extracted telephone number of the called party; wherein the short message service message or the multi-media service message is transmitted through the message gateway according to the telephone number if a telephone corresponding to the telephone number is capable of transmitting/receiving the short message service message or the multi-media service message, otherwise the converted message is transmitted through the SMS/MMS gateway to the called party according to the ID information.