Cellular telephone operators are currently required to provide caller localisation information for use by emergency services. Localisation fields appended to Call Detail Records can now also be exploited for commercial purposes, such as: new network services; subscription fraud detection; customer behaviour monitoring; health care monitoring; law enforcement and forensics; and national and international security. The talk reviews cellphone localisation technology via: 1. A survey of location based services and applications; 2. An overview of localisation techniques with an example; 3. A GSM trace-mobile demonstration of types of information available