A brief guide to IMEI, ESN, and other numbers on your phone

A brief guide to IMEI, ESN, and other numbers on your phone



All mobile phones, as well as other cellular-connected devices such as tablets, have a unique serial number. There have been a few different names and formats for these serial numbers over the years, including ESN, MEID, and IMEI. Keep reading to learn more about each of these serial number formats, and about why they are so important.

Table of Contents:


What is an IMEI number and how do they work?

IMEI stands for International Mobile Equipment Identity. Essentially, the IMEI is a unique identifier for cellular-connected devices such as phones and tablets. The IMEI number consists of 15 digits (all numbers). Depending on the make and model of your phone, you may even have more than one IMEI.

For example, if you navigate to the settings on your iPhone, you’ll likely find a Primary IMEI and a Digital SIM IMEI. These both are able to identify your phone, and the difference between the Primary and Digital really just comes down to whether you insert a physical SIM card or use the eSIM (electronic SIM) functionality built into the iPhone.

The IMEI number allows wireless carriers to identity devices being used on their networks. Carriers use the IMEI to associate a device with a particular user account. The IMEI number is used to record the device status and activity. Carriers can also use the IMEI to prevent a mobile device from being used on a network if it has been reported as lost or stolen.

How to tell if a phone is unlocked with the IMEI?

Having an unlocked phone means it can be used with different wireless carriers. The simplest way to determine if your smartphone is unlocked is by trying to use a SIM card from another carrier. If the SIM is recognized and the phone connects to the network, it is unlocked. You can also use the IMEI to determine if the phone is unlocked. You can find the IMEI in the phone settings, and then call your current wireless carrier and ask if the phone is unlocked for use with other carriers.

Why check a phone’s IMEI?

If you are buying a brand-new phone from a manufacturer like Apple, or directly from your wireless carrier — you really shouldn’t worry too much about the IMEI, aside from when you are getting your phone activated with your carrier. On the flip side, if you are buying a phone from another person — you will want to check the IMEI.

Checking the IMEI of a phone is important because it helps determine whether the phone has been reported as lost or stolen. An IMEI check can also be used to see if a phone is compatible with a certain wireless carrier, and to detect any possible carrier activation issues, such as if it is still active on another persons account.

An IMEI number is important and it should be safeguarded. Because of this, not everyone is willing to share an IMEI publicly, or even with just another random person. This doesn’t mean you shouldn’t buy used phones — after all, buying used phones is a great way to save money. What it does mean is that you should buy your used phone from a trusted marketplace such as Swappa, or a trusted source such as a friend or family member.

Here on Swappa, sellers are not permitted to share an IMEI with another user before the device has been purchased. However, sellers are required to enter the device IMEI when they create a listing to sell their device. A Swappa staff member then checks the IMEI during the listing review process. Assuming the IMEI check comes back clear with no issues, the listing can be approved. If there are any issues, the listing will not be approved.

If you are buying a phone from an unknown source, you should make sure to get and check the IMEI number before handing over any money. Fortunately — it is easy (and free) to check an IMEI. To run an IMEI check, you first need to locate the IMEI number(s) in the phone settings. Once you have the IMEI number, you can use Swappa’s free ESN check to determine whether the IMEI is clean or if there are any reported issues.

What is an ESN number and how is it different than an IMEI?

ESN stands for Electronic Serial Number. ESNs first came to use in the early 1980s, and they were used as a way to uniquely identify mobile devices. More recently, ESNs were used to identify devices with CDMA carriers such as Sprint and Verizon. An ESN was either an 8-digit hexadecimal number or an 11-digit decimal number. New and unique ESN numbers have since been exhausted, and a new format, MEID (Mobile Equipment Identifier), was created in the mid-2000s.

The ESN and IMEI are similar in that they are both used to uniquely identify a mobile device, but there are a few differences. The ESN was used by CDMA carriers such as Sprint and Verizon, and the IMEI is used by GSM carriers such as T-Mobile and AT&T. The ESN and IMEI also differ in format, with the IMEI being a 15-digit number that is made up of 14-digits with one check digit.

What is a MEID and how is it different than an IMEI?

MEID stands for Mobile Equipment Identifier. The MEID number is a unique 14-digit identifier for smartphones and other devices connected to a cellular network. The MEID number was commonly used by CDMA carriers, such as Sprint and Verizon. You will still see mobile devices with a MEID number and you can still run a MEID check, but the IMEI (International Mobile Equipment Identification) is more commonly seen at this time. The main difference with MEID vs IMEI is the number of digits, with the MEID having 14 hexadecimal digits and the IMEI having 15-digits (14-digits with one check digit).

What does a bad ESN, MEID, or IMEI mean?

On a simple level, the ESN, MEID, and IMEI are all serial numbers used to identify your mobile device. If your device has a bad serial number, you will not be able to get it activated for use with your wireless carrier. A serial number can show as being bad for several reasons, such as the phone having been reported as lost or stolen, or if the serial number has an outstanding balance with the carrier. A serial number can also show as bad if it is still active on another person’s wireless account.

Once a serial number has been reported as lost or stolen, it can be difficult to get the device status cleared. However, other issues such as an outstanding balance can be cleared once the balance has been paid in full. Similarly, if the ESN, MEID, or IMEI check initially shows the device is still associated with another person’s account, that can be easily cleared once the carrier is notified and the device is removed.

You can run a free online ESN check using Swappa’s IMEI Check / ESN Check tool.