The Difference Between ESN & IMEI

By Steve McDonnell

Your mobile carrier can block a lost or stolen phone by IMEI or ESN.
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There are two primary mobile service provider technologies in use around the world: Code Division Multiple Access and Global System for Mobiles. A mobile phone is manufactured to support either CDMA or GSM, but not both. Phone manufacturers assign a unique identification number to each handset they produce according to the technology it supports. The GSM identification number is called an International Mobile Equipment Identification and CDMA's version is called an Electronic Serial Number.

Mobile Technology in the United States

The division of mobile service technology in the United States is inverse to that seen in the rest of the world. Five of the seven largest mobile service providers in the U.S. use the CDMA technology: Verizon, Sprint, MetroPCS, Cricket and U.S. Cellular. The remaining two providers, AT&T and T-Mobile, use GSM. Outside the U.S., more than 80 percent of carriers use GSM, giving it about a 73 percent global market share.

IMEI Numbers

The IMEI number on a GSM network is associated with a particular mobile device and does not identify an individual subscriber. Instead of associating subscribers with IMEI numbers, GSM uses a Subscriber Identity Module card to store a customer's information. When a customer wants to switch phones on a GSM network, he can simply remove the SIM card from one device, insert it into another device and begin making calls.


CDMA does not use a SIM card. As a result, an ESN on a CDMA network is associated with both a device and a customer. When a customer activates new service or switches phones, the mobile service provider must associate her account with the new ESN before she can start making calls.

Stolen Phones

If your mobile phone is lost or stolen and you report it to your mobile service carrier, a carrier using CDMA can flag the ESN as stolen and prevent anyone from using your account until you switch to a new phone. Mobile service providers who use CDMA can also deny access to your phone if you haven't paid your bill by blocking the ESN on their networks. Prior to 2012, GSM technology in the U.S. enabled a service provider to block a subscriber's account by the information stored on the SIM card, but did not enable a carrier to block a phone by IMEI number.

Blocking by IMEI and ESN

In response to pressure from the U.S. government to take a more active role in deterring mobile phone theft, AT&T modified its GSM system in the U.S. in 2012 to be able to block a phone by IMEI number. T-Mobile completed its modification in early 2013. At the government's request, the seven largest mobile service providers agreed to create a database of stolen IMEI numbers and ESNs that can be shared among all providers to prevent a thief from using a stolen phone on a different provider's network. As of 2013, AT&T and T-Mobile share a single IMEI block list.