A method and system of providing an unambiguous connection between a first user equipment and a second user equipment in a combination of a circuit switched call and a packet switched multimedia session. The method comprises to construct an equipment identifier by a first user equipment, wherein the equipment identifier distinguishes the first user equipment from any other user equipment of a same user and comprises a uniform resource name. Further, the first user equipment is registered in a session control protocol environment by sending the equipment identifier to a session control protocol registrar. In addition, a uniform resource identifier is returned by the session control protocol registrar, wherein the uniform resource identifier routes to a session control protocol application, and wherein the uniform resource identifier includes the equipment identifier as an opaque parameter. Finally, the opaque parameter is advertised by the first user equipment in a circuit switched call.