There are several places to find these numbers, like in the Settings menu, on the physical device, in iTunes, or on the original packaging, some of listed below:
1. Go to your iPhone dialler keypad and type *#06# (star-hash-zero-six-hash). The IMEI number will appear on your screen.
2. You can find the IMEI on the SIM tray of most of iPhone devices.
3. In the iPhone menu, go to Settings >General >About. The IMEI number should be listed on the screen.
4. Connect your iPhone to iTunes on a computer. On the information page, click on the phone number. This tells you several pieces of information about the iPhone, one of which is the IMEI number.
Still uncleared? Click here if you want to learn more about IMEI numbers