The Indian Telecom Ministry has implemented a ban on mobile phones without valid EMEI numbers, cutting potentially 25 million devices off its networks. Handsets that don't have a valid code will no longer be able to send or receive calls or text messages.
IMEI stands for "International Mobile Equipment Identity", and as the name suggests, it identifies a mobile device. India was concerned after it was discovered that terrorists who had conducted bombing attacks had used devices without valid IMEI numbers.
As a result, the Department of Telecom implemented a cut-off date - 1 December 2009 - after which devices without valid numbers would no longer be able to be used. In the UK, the number is often used to block stolen mobile phones, rendering them useless. As a result, it is an offence in the UK to change the IMEI number of a phone, or possess equipment that can change it.
The consequences of the ban will be interesting to watch. The majority of phones that the Indian ban affects are counterfeited or stolen handsets. That'll suddenly create immense demand for new handsets at phone shops and a whole pile of dead phones that need recycling. Both of those things could prove problematic for the country.