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. Writer Bio

The Difference Between ESN   IMEI - 43