This apparatus operates to discern temporal and spatial anomalies in the use of subscriber numbers in the cellular mobile telephone system. The detection of such anomalies is typically indicative of attempted fraudulent access to the cellular mobile telephone system via cloning of valid subscriber numbers....http://www.google.se/patents/US5335265?utm_source=gb-gplus-sharePatent US5335265 - Apparatus for detecting and preventing subscriber number cloning in a cellular mobile telephone system
