The IMEI (International Mobile Equipment Identity) number of a mobile handset is a 15 digit number unique to a mobile handset. Just key in *#06# on your cellular phone and it will display its IMEI number in most phones. Note it down safely. It is also usually printed on the compliance plate of the handset. In fact each GSM mobile phone is assigned a unique IMEI code when it is produced. If you know the IMEI code of a mobile phone, you can check information regarding manufacturer, model type, date and country of approval.IMEI number can help in tracking or blocking your mobile phone if it is lost. When a phone is switched on, the IMEI number is transmitted and checked against a database in the network's EIR (Equipment Identity Register). The EIR has three categories namely the "white lists", "grey lists" and "black lists". The operator can block a handset by putting it in black list. Also by using Global Positioning System an operator can track the handset user also. But the use of these lists and technologies is at the operators' discretion. Generally operators provide these services in case of special investigations only.