"There is a small size programme of less than 2Mb called 'Tinyumbrella'. Download it and run, it has a row for IMEI and it will show you. Besides it saves your SHSH just in case you have installed a newer version of Apple's IOS and you want to go back to the previous version, and the most interesting thing about it is that it does not install anything on your system.
Just go to tinyumbrella.com and download it. I hope this helps!"
The IMEI number (as well as the serial number) of the iPhone 4 is written on the sim card tray. Eject the sim card tray and look on it. You will find the numbers.