System for managing the identities of mobile stations roaming between mobile radio networks, operating within a private mobile radio network, constituted by one or more base transceiver stations (BTS; Node B) and by a reference base station controller (BSC; RNC), which realize a normal base station subsystem (BSS; RNS) within the public mobile radio network, characterised in that upon registration of the roaming mobile station (MS), authorized to access the private mobile radio network, the system (VIM) simulates, from the base station subsystem (BSS; RNS) towards the mobile switching center (MSC) of the competent network switching subsystem (NSS), the behaviour of the mobile station, whereto it has associated the identity profile selected from a group of identity profiles held by the operator of the visited network, and in wholly similar form, from the mobile switching center (MSC) towards the base station subsystem (BSS), the system (VIM) simulates the behaviour of the competent network switching subsystem (NSS) during the salient steps of the registration of the roaming mobile station, in such a way as to assure the correct execution of the procedure itself.