Method for identifying a radiocommunications network of the host type of a user terminal (4A, 4B) from among at least two networks (1, 2) forming a radiocommunications infrastructure that comprises: - a base station shared by the at least two networks (1, 2), said base station being able to: ∘ provide the radio transmission and reception with said user terminal (4A, 4B) being located in a cell attached to said base station, and ∘ route data between said user terminal (4A, 4B) and each one of said at least two networks (1, 2), - a network core (1A, 2A) for each one of said networks (1, 2), each network core (1A, 2A) comprising: ∘ means for authenticating and controlling (6, 10) user terminals (4A, 4B), and ∘ a database (7, 11) containing information concerning the access rights of user terminals (4A, 4B) to one of the said networks (1, 2), each user terminal (4A, 4B) having a unique user identification code comprising: - a first network identifier code, and - a second user identifier code of the host network, said method being characterised in that when said user terminal (4A, 4B) is located in a cell and said user terminal (4A, 4B) transmits for the first time a request for attaching to one of the said networks (1, 2) by means of its unique identification code, said method comprising the following steps: - checking the access rights of said user terminal (4A, 4B) to said radiocommunications infrastructure according to said first network identifier code, said first network identifier code being shared for said at least two networks (1, 2), - according to a step referred to as pre-decoding and routing, identifying the host network of said user terminal (4A, 4B) by means of said second code and routing the request for attaching from said user terminal (4A, 4B) to means for authenticating and controlling (6, 10) of the host network identified which are able to authenticate said user terminal (4A, 4B). - a base station shared by the at least two networks (1, 2), said base station being able to: ∘ provide the radio transmission and reception with said user terminal (4A, 4B) being located in a cell attached to said base station, and ∘ route data between said user terminal (4A, 4B) and each one of said at least two networks (1, 2), ∘ provide the radio transmission and reception with said user terminal (4A, 4B) being located in a cell attached to said base station, and ∘ route data between said user terminal (4A, 4B) and each one of said at least two networks (1, 2), - a network core (1A, 2A) for each one of said networks (1, 2), each network core (1A, 2A) comprising: ∘ means for authenticating and controlling (6, 10) user terminals (4A, 4B), and ∘ a database (7, 11) containing information concerning the access rights of user terminals (4A, 4B) to one of the said networks (1, 2), ∘ means for authenticating and controlling (6, 10) user terminals (4A, 4B), and ∘ a database (7, 11) containing information concerning the access rights of user terminals (4A, 4B) to one of the said networks (1, 2), - a first network identifier code, and - a second user identifier code of the host network, said method being characterised in that when said user terminal (4A, 4B) is located in a cell and said user terminal (4A, 4B) transmits for the first time a request for attaching to one of the said networks (1, 2) by means of its unique identification code, said method comprising the following steps: - checking the access rights of said user terminal (4A, 4B) to said radiocommunications infrastructure according to said first network identifier code, said first network identifier code being shared for said at least two networks (1, 2), - according to a step referred to as pre-decoding and routing, identifying the host network of said user terminal (4A, 4B) by means of said second code and routing the request for attaching from said user terminal (4A, 4B) to means for authenticating and controlling (6, 10) of the host network identified which are able to authenticate said user terminal (4A, 4B). - checking the access rights of said user terminal (4A, 4B) to said radiocommunications infrastructure according to said first network identifier code, said first network identifier code being shared for said at least two networks (1, 2), - according to a step referred to as pre-decoding and routing, identifying the host network of said user terminal (4A, 4B) by means of said second code and routing the request for attaching from said user terminal (4A, 4B) to means for authenticating and controlling (6, 10) of the host network identified which are able to authenticate said user terminal (4A, 4B).