IMEI number is a unique 15-digit code that can identify a handset to a GSM network (prevents stolen handsets from being used and allows lawful interception) - every time a call is made, the IMEI number shows on the operator’s network. DoT has asked service providers to equip networks with Equipment Identity Register (EIR) to check if calls are being made from genuine handsets -
Operators in order to achieve the same will have to invest more in equipments
What the DoT is trying to do is to block all calls with zeroes as IMEI numbers or from blacklisted numbers. That adds extra load on networks. There are so many combinations of non-genuine IMEI numbers that it is extremely difficult to block them. Network upgradation is required to block all such calls and not all of our multiple equipment vendors are equipped to do it, [ET]
In toto, close to 25 million phones in India do not have IMEI number and are expected to be thrown out of the network by Jan 6, 2009.