A method for The method for transmitting a message between a mobile communication system and at least a core network, the mobile communication system having a mobile station and a radio network, the method comprising the steps of: a) at the radio network, discriminating an operating type of a core network(s) coupled thereto; b) at the radio network, generating and transmitting a system information message having core network operating type information and information related to the core network; c) if two or more core networks are coupled to the asynchronous mobile communication system, at the mobile station, selecting one core network to be communicated with, based on the system information message; d) operating a call control entity and a mobility management entity according to an operating type of the selected core network; and e) communicating messages between the mobile station and the radio network, the message having a different data format according to the operating type of the selected core network.