A cellular phone unit, upon turning from a standby mode to a data communication mode, responds to a user's instruction of location positioning to turn from the data communication mode to the dormant mode, receives again base station identification numbers from several base stations through a paging channel, and designates again one of the base stations with the received identification numbers as the base station of primary communication with the phone unit. The phone unit can send the identification number of the proper base station of primary communication to a location information server even in case the phone unit is instructed by the user to commence the location positioning after it has moved from the location where it had commenced the data communication.