SIP type signal protocol for a mobile communication network (N), comprising an invitation signal message (MI) “INVITE”, intended to set-up a “Push to Talk” type communication session between a calling communication client (A) and one or several called communication clients (B, C), and containing the logical address of the calling communication client and an address of the called communication client(s).The signal protocol is innovative in that the invitation signal message (MI) also contains a visiting card associated with a user of the calling communication client (A).