Several ways to find your iPhone International Mobile Equipment Identity (IMEI)

On the SIM tray of iPhone 3G, iPhone 3GS, and iPhone 4 (GSM model):

iPhone About screen:

You can find your iPhone IMEI in the About screen on your iPhone. From the Home screen, tap Settings > General > About and scroll down.

iPhone packaging:

If you still have the device's original packaging, you can find your iPhone serial number and IMEI or MEID printed on the barcode label that's affixed to the packaging.