They are also asked to verify the 15-digit IMEI (International Mobile Equipment Identity) code of legal devices.

BBC: Uganda delays fake mobile switch-off date until 2013

Fakes usually do not have an IMEI code or have copied another one.

BBC: Uganda delays fake mobile switch-off date until 2013

Law enforcement agencies had also complained that some of the devices used duplicated IMEI (International Mobile Equipment Identifier) codes, making it difficult to track down users suspected of using their handsets to plan crimes.

BBC: Kenya to switch off 'fake' mobile phones