Indian operators are expected to block several million mobile phones tomorrow (1st Dec) as a government ban on handsets without a valid IMEI comes into effect. Earlier estimates had suggested that as many as 25 million handsets were being used without an IMEI number, although this will have shrunk noticeably over the past few months as the deadline approached.

Since the ban was proposed, the operators have been offering a reprogramming service to insert a valid IMEI into the handsets, but it is thought that there are still millions of potentially illegal handsets in use. Due to the scale of the operation, the government has already delayed implementing the ban on two previous occasions, but has said that it will not permit any more delays.

Mobile phones without an IMEI are typically low-end handsets from smaller Chinese phone manufacturers who cut costs by skipping the IMEI programming stage.

Although the serial number does not affect the billing, which is managed by SIM identities, it does add an extra layer of proof for the police if checking who made a phone call from a specific handset. The issue became a serious topic after such phones were allegedly used by terrorists, and the lack of unique IMEI made it impossible to prove who made or received specific phone calls as they couldn't be traced to a specific handset.

A ban on importing handsets without unique IMEI's was imposed earlier this year.