The subject innovation relates to a system and method for routing in a base station system a message received from a mobile communication device to a core network. The base station system may be connected to at least two core networks and an identifier being assigned to each core network. An exemplary method comprises receiving in the base station system the message from the mobile communication device together with an identifier assigned to a first core network of the core networks. The identifier may be read in the base station system. The exemplary method also comprises forwarding the message from the base station system to the first core network based upon the read identifier.