If you’re in the market for a cellphone, especially a used one, you’ll hear a lot of talk about ESNs with an emphasis on whether or not the phone is “clean”. What exactly does acronym stand for and what does it mean if the phone is clean or not?

Dear How-To Geek,

I’m recently out of contract with my cell carrier and I really don’t want to get back into a lengthy contract just to upgrade my phone. As such, I’ve been searching eBay and Craigslist for used phones I could add onto my account without getting stuck in another 48-month contract. One term that comes up in just about every search is “ESN” and sometimes “MEID”, and always in the context of whether or not that thing is “clean”. This is the first time I’ve done anything other than just walk into the local cell store and sign some paperwork to get a new phone, so I’d like to do this smart and not end up with a phone that doesn’t work. So what’s this clean ESN business and how do I make sure I’m getting a good used phone?


Acronym Averse

Let’s start with the basics and then move onto how you can use that knowledge to protect yourself as a consumer. ESN stands for Electronic Serial Number and was introduced as a unique identification number for all mobile devices by the FCC in the early 1980s. Electronic Serial Numbers were attached to CDMA devices (CDMA just refers to the radio type in the mobile device — Sprint phones, for example, are CDMA devices). Later, the ESN system was revised into the MEID (to account for a shrinking pool of available ESNs), and still used for CDMA devices.  Another number to be aware of is the IMEI (Interational Mobile Station Equipment Identity) number, which is the ESN equivalent for GSM (e.g. ATT&T) based phones.

Although ESN, MEID, and IMEI are distinct identification standards, ESN has come into popular usage as a catch all for the serial number (in whatever format it may be in) for the phone in question. As such, you’ll see references to the ESN number of an ATT-branded iPhone even though that phone actually as an IMEI, not an ESN. In fact, we’re going to use it in the same fashion for the rest of our response unless we’re explicitly referring to a specific identification number system.

Now, why does the ESN matter to you, the consumer? Cellphones are valuable and carriers have a vested interest in them (after all, the real price of that iPhone you just picked up isn’t actually $99, the carrier is heavily subsidizing your phone’s cost via the extended contract you just signed). They use ESNs as a tool for tracking phones and, when need be, banning phones from their network.

There are two principal reasons why an ESN would be blacklisted: the phone was reported stolen, or the phone is attached to a cellular carrier account with an outstanding  balance.

The first scenario is actually fairly rare, many U.S.-based cellular carriers didn’t actively use ESNs this way for the longest time. In fact, AT&T only started recording and blacklisting the IMEI numbers of stolen phones in November of 2012 and only after pressure from government agencies. The second scenario, failure to pay an account balance or skipping out on a contract, is much more common. The majority of phones you encounter with a “bad ESN” earned that blacklist status because the previous owner of the phone left the company with a huge unpaid bill.

So, how can you use this information to protect yourself? You can refuse to purchase a phone without a clean ESN. When it comes to eBay listings, it’s tricky to completely protect yourself as you are at the mercy of the seller in many regards. First, you should try to purchase from eBay sellers that obviously specialize in turning over phones as they’re the most likely to have run the ESN and they’re invested in not having to deal with the hassles of returns and customer service headaches. Contact them and request the phones ESN so you can check it yourself before placing your bid. If they refuse, shop elsewhere; it’s unreasonable to expect you to bid several hundred dollars on a phone without knowing if you can even activate it with your carrier.

When purchasing a phone in person, one of the easiest ways to avoid a headache is to meet the person you’re purchasing the phone from at a store that services the cellular provider you plan on using the phone with. In some cases, this is the only way to get an official company ESN check. Sprint, for example, no longer does ESN checks over the phone.

In the store, you can hand the phone right over to the company rep and ask them to check if the phone is clear for use on their network. Suggesting you meet at the store so you can activate the phone right away is a great way to get rid of scammers right off the bat; they won’t want to meet you at the store if they have a bad phone.

What if you don’t have a local store you can stop by? In this case, you’ll need to check the ESN yourself. On 99.99% of phones, the ESN (or equivalent) is located under the battery on a sticker. Open the case, pop the battery, and look at the number. On devices that are sealed, like the iPhone, you can find the identification number in the system menu.

Once you have the number, you can get to the bottom of things in one of two ways. You could call the support line for the specific carrier you want to use the phone on. This is by far the best way to go about it. It takes more time than the web-based method we’re about to show you, but it gives you direct confirmation that the phone will work on the network you want to use it on. It’s important that you are specific in who you call. Let’s say, for example, you have a Sprint branded phone that you want to use on Ting, a Sprint reseller. Call Ting, not Sprint. If the phone has been activated before as a Ting phone, then Sprint will have permanently banned the phone and will report that it has a bad ESN even though Ting will happily activate it again. The same goes for most other major carriers and their resellers; the major carriers will frequently blacklist phones that have been used with their resellers, but the resellers have no problem with them.

If you don’t want to/can’t call the carrier, there are quite a few ESN check websites out there. These sites will give you a good idea if the ESN is clean or not. While we’ve never had any false positives using an ESN check web site, we do want to stress that the only truly foolproof method is to call the carrier.

For web-based checks, some of the more popular/reliable sites are Swappa (a phone/gadget purchasing company, their tool is seen in the screenshot above) and CheckESNFree. As a general rule, the more information online ESN checkers return, the better. In the screenshot above we get a valid ESN check, a carrier, and even a model  number. With older phones or phones not in the system, you’ll get a simple “this is a valid ESN” type response, but no specific information.

Armed with the knowledge of what an ESN is and how to use one to confirm the status of a phone, you’ll be in a much better position to protect yourself from scammers and getting stuck with a bad phone.

Profile Photo for Jason Fitzpatrick Jason Fitzpatrick
Jason Fitzpatrick is the Senior Smart Home Editor at How-To Geek. He has over a decade of experience in publishing and has authored thousands of articles at How-To Geek, Review Geek, LifeSavvy, and Lifehacker. Jason served as Lifehacker's Weekend Editor before he joined How-To Geek.
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