The ESN is the electronic serial number, and if it isn't clean, you can't get a service contract for that device.
The term "ESN" in an abbreviation for "electronic serial number." Every cellular phone produced over the last few years has a uniquely identifiable serial number that is continuously relayed to the nearest cell tower, which, in turn, transmits the information to a central computer that identifies your particular account. The communications giants that provide your "can't live without it" device usually require you to sign a one- or two-year contract, during which time they make up for the discounted cost of the phone or PDA, your personal digital assistant, be it an iPhone or a Blackberry or any number of other devices that are wireless-enabled.
Where do I find my device's ESN?
If you purchase a device new, all that information is located on the box, generally on a sticker with a miniature barcode. Unless you have excellent vision, you will probably need a magnifying glass to read it. You should record the number somewhere, in case your phone is lost or stolen so that you may report it to your carrier to protect yourself. If you are a hoarder, make the box part of your hoard so that it is there when you need it, at the bottom of one of the shopping carts in your garage.
In the event you acquired your phone secondhand or just discarded the box at the phone store, don't fret. By opening the back of your phone and removing the battery, you will find the same information. If your phone left you, of course, you will not have that information, but your carrier will be able to match that information to your actual phone number and verify you as the legitimate owner.
What does a clean ESN mean?
When you first buy and activate your device, it has a "clean' ESN, and it will remain clean as long as you don't fail to pay your monthly bill during the contracted time. If you try to switch carriers with your phone before your contract is up, or you have unpaid bills, you will not be able to reactivate your phone until such time as you either buy out your contract or pay your bill. If you want to check if your ESN is clean, there is a free service online.
What if you have a soiled ESN?
Many times, people purchase cell phones or PDAs secondhand without having a clue as to whether the device is stolen, found in a bar or simply being sold while it still has an active or unpaid contract balance.
Normally, the first inkling you have of that is when you go the phone company the unit is branded with and try to activate it. They will politely refuse and of course offer you the latest in wireless gimmickry available as a two-year contract, if you have good credit.
Is there a way to unlock the cell phone?
There are always electronic wizards capable of accomplishing that hack, but it is a gray area of the law, as unscrupulous operators may unlock stolen cell phones and contribute to other illegal activities. Therefore we will not get into that subject.