All the phone operator has announced to its customer that the sim card will not work if you don not have a correct IMEI Number. All the Mobile not having a IMEI number will not work from December 13,2009.You can check your IMEI numbet by pressing *#06#. Most of the China/Korean sets have either no IMEI or Invalid IMEI number. So you need to change the mobile or register a IMEI number at Govt. approved centres. to get a valid IMEI number for your mobile .For airtel customer, you can know the Govt approved centers for registering IMEI by sending “HS (pin code)” to 121(toll free). Eg: HS 600017 to 121.
You(who is handing over the mobile) are requested to photo and address verification certificate like driving license or ration card or passpost etc. It costs INR199( Indian Rupees )