Find the IMEI number of your mobile phone
The International Mobile Station Equipment Identity or IMEI is unique number to identify mobile phones as well as satellite phones.
Every mobile phone, GSM modem or device with a built-in phone / modem has a unique 15 digit IMEI number. The IMEI number is used by a GSM network to identify valid devices and therefore can be used for stopping a stolen phone from accessing that network.

If your mobile phone is lost , first thing you have to do is to inform nearest police station and contact your mobile service provider to block the SIM. Inorder to register complaint with the police station, you should know your mobile phones' IMEI number, else it would be very difficult to track.
To know the IMEI number, perform any of given steps:
1. Dial *#06# , on entering the second "#" character, your phone IMEI number will be displayed on your mobile phone screen.
2. IMEI number can be found printed inside the battery compartment of the phone.
3. Check the cover of your mobile phone, the IMEI # may be printed in that.
4. It can be found from the Setting > About device section of your phone.
If you are using multiple SIM cards then there will be more than One IMEI numbers depending on number of SIM's you use. The IMEI is only used for identifying the device , it has no relation with subscriber.
You can verify some information about your mobile device by entering the IMEI number here www.imei.info.