The Electronic Serial Number, also known as the mobile equipment identifier, is an essential piece of identifying information for your phone, so Motorola places it in numerous locations, including the packaging the device comes in. Even if you don’t have the box, finding the ESN is a simple process.
On the Phone's Body
The easiest place to find the serial number is on the sticker on the back of the phone. If this happens to peel off, you can find the number inside the door of the SIM/SD card compartment on the side of your device.
In the Phone Settings
You can also bring up the serial number in the phone's settings menu. Tap “Applications | All Apps | Settings | About Phone | Status.” The ESN is located under the MEID heading.