Method of attaching and authenticating a user terminal of a radio communications network of host type to a telecommunications network of visited type, said host network comprising in particular host means for attaching to a packet network and said visited network comprising: - at least one visited base station able to ensure the radio transmission and reception with user terminals (4A, 4B) lying in at least one visited cell attached to said visited base station; - visited means for authenticating and checking the user terminals (4A, 4B) able to authenticate the user terminals (4A, 4B) attached to said network; and - at least one visited distribution gateway ensuring the radio reception and transmission with said at least one visited base station; said method being such that the host network and the visited network have a network identifier code that is common at least with the two networks, with each user terminal belonging to the host network has a first user identifier code comprising, on the one hand, the network identifier code that is common at least to the host network and to the visited network; and on the other hand a second user identification code of the host network, and when the user terminal belonging to the host network is lying in a visited cell of the visited base station, said method comprises the following steps: - accessing the visited network from the user terminal of the host network, by means of the common network identifier code; - authenticating, in the visited network the user terminal by means of the second user identification code of the host network with at least one database (14A, 14B) comprising information relating to the access rights of users of the user terminals (4A, 4B) to the visited network; and - establishing an access channel dedicated to the user terminal of the host network between the visited distribution gateway and the host means for attaching said method being characterised in that said second user identification code of the host network comprises: - an identification code of a service zone of the host network; - an identification code of a category of users of the host network; and - a third user identification code within the service zone of the host network and of the category of users of the host network, with the authentication of the user terminal of the host network in the visited network being carried out by means of at least one of the three identification codes of the second user identification code of the host network. - at least one visited base station able to ensure the radio transmission and reception with user terminals (4A, 4B) lying in at least one visited cell attached to said visited base station; - visited means for authenticating and checking the user terminals (4A, 4B) able to authenticate the user terminals (4A, 4B) attached to said network; and - at least one visited distribution gateway ensuring the radio reception and transmission with said at least one visited base station; - accessing the visited network from the user terminal of the host network, by means of the common network identifier code; - authenticating, in the visited network the user terminal by means of the second user identification code of the host network with at least one database (14A, 14B) comprising information relating to the access rights of users of the user terminals (4A, 4B) to the visited network; and - establishing an access channel dedicated to the user terminal of the host network between the visited distribution gateway and the host means for attaching - an identification code of a service zone of the host network; - an identification code of a category of users of the host network; and - a third user identification code within the service zone of the host network and of the category of users of the host network,