Your phone's electronic serial number (ESN) is unique. The number cannot be changed like your cell number or the network ID your cell phone company uses to identify your phone on the network. Obtaining your ESN allows you to confirm the authenticity of your cell phone with customer service reps and is also vital in moving your cell number to a new handset.
Check your cell phone's box for the ESN. Electronic serial numbers are printed onto a sticker and located somewhere on the box--usually on the opening flap. You'll see two ESN numbers on the sticker. The one you want will be labeled "DEC ESN" followed by the serial number.
Find your ESN on the phone itself if the box isn't available or the sticker containing the ESN is missing. First, shut off your cell phone. Then remove the battery cover and the battery itself. The ESN will be located on the back of the phone where the battery was. Locate the string of numbers labeled "ESN DEC."
Locate your ESN through your cell phone by hitting the "Settings" option, then the option labeled "Phone Info." Scroll through the list of technical data on your phone to find the ESN.