The ESN (Electronic Serial Number) on a cell phone (IMEI for GSM phones) is unique to each phone and is what’s used to tie the phone to the user’s carrier account. Not only that, but lost/stolen devices have their ESNs “blacklisted” at the carrier and therefore cannot be activated again.
For this reason you have to make sure that any used cell phone you plan to purchase has a “clean” or clear ESN. This means that it’s no longer tied to a persons account and hasn’t been blacklisted by the carrier. If the ESN is still tied to a subscribers account, or is blacklisted, it cannot be activated.
So what are the best steps to do this?
1) Make sure the seller makes an assertion that the ESN is “good”, “clean”, “ready to activate” or similar. If this is listed in the ad, you have a recourse in the event that you buy the phone and the carrier will not activate it based on the ESN. If the seller doesn’t state this, contact them via email or other (preferably written) manner and ask them. Any honest seller is more than willing to make an assertion about an ESN.
2) If you have the ESN itself, contact the carrier and ask them to make sure the device can be activated. Carriers have no problem checking an ESN for a customer. If the carrier gives you anything other than and all-clear, don’t make the purchase.
The other thing to be careful about is physical damage. If you’re buying a used phone, a certain amount of physical damage is expected. Cosmetic issues such as worn paint, light-to-medium scratches, and minor chips, or dents to non-functional parts are expected.
Make sure to carefully read the ad for any mention of functional issues or missing parts. Issues such as non-working or missing keyboard keys, cracks to anything other than the battery cover, non-working or cracked display, non-functioning digitizer (touchscreen), non-functioning or improperly-functioning speaker or microphone, and a leaking/bulging/damaged/otherwise non-functioning battery are considered functional damage and are serious enough to give the buyer recourse against the seller if they are not disclosed.
A non-functional charger could be considered functional, but standardized chargers are inexpensive enough that a buyer may want to consider purchasing a replacement charger themselves, rather than taking issue with the seller. If the phone requires a non-standard charger, contact the seller and see if they would be willing to either provide a replacement charger or provide you a refund for the amount of a reasonably-priced replacement charger.
Test all of the phones functions as soon as possible. If you wait to test the phone and find out later that something doesn’t work, you may be out of luck.
Lastly, if you are activating your newly-purchased phone, you may want to consider adding a carrier-provided insurance or protection plan to your device. If your device fails down the road, the carriers plan will be able to provide inexpensive repair or replacement, regardless of the fact that you acquired it second-hand. Check with your carrier for information on their policies.
If you have any thoughts to share on the above, please feel free to post them in the comments below. Thank you!