The present invention relates to a communications system for mobile radio telephony comprising mobile devices, comprising modules which can be inserted into the mobile devices, with at least one subscriber territory being fixed inside the total territory covered by the communications system, within which subscriber territory communication takes place from and/or to the mobile devices under special conditions, and comprising means by which it can be determined whether the mobile device is located inside the subscriber territory. In accordance with the invention, the means are arranged on the module or in a determination unit which can be accessed by means of remote polling. The present invention furthermore relates to a method of operating a communications system for mobile radio telephony.