registering a mobile station in a private mobile network cooperating with a public land mobile network enables necessary ms information to be registered with an incoming call of the ms without a complicated procedure when the ms registers with the private mobile network and includes : receiving an origination message transmitted from the ms through a private base transceiver station included in the private mobile network ; extracting a function code , a mobile directory number , and ms information from the received orm ; examining ms registration information stored in the phlr using the extracted mdn when the function code is a registration function code ; and updating and registering the ms registration information using the extracted ms information when the examined ms registration information is in a registration initialization pattern .