The invention relates to an instantaneous messaging system for mobile terminals comprising one or several instantaneous messaging service servers (S1, S2) able to deliver instantaneous messaging services to mobile terminals (TA, TB1, TC1, TD1, TB2, TE2, TF2) connected to said servers and of which the users (A, B1, C1, D1, B2, E2, F2) have opened an instantaneous messaging session, and a virtual presence server (100) independent of the existing instantaneous messaging service servers (S1, S2), said virtual presence server being connected to at least one mobile client terminal (TA) and to at least one of the existing messaging servers (S1, S2) in such a way that the information intended for or sent by said mobile client terminal transits by said virtual presence server, wherein the instantaneous messaging service servers (S1, S2) are configured to transmit contact lists intended for mobile client terminal (TA), said lists being intercepted by the virtual presence server (100), the latter comprising a means to aggregate the different contact lists received and only manage a single list (110) in which are registered the identities of the different users (B1, C1, D1, B2, E2, F2), without distinction as to the community that said users are members of.The invention also relates to a method making it possible to manage different contact lists of a single user in an instantaneous messaging session.