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(pronounced as separate letters) Short for electronic serial number, a unique identification number that every cellular phone has and is assigned by the specific manufacturer. When a cellular call is placed on a mobile telephone, the ESN is transmitted to a base station, and the number is used to authenticate the validity of the phone in respect to the cellular service the phone is attempting to use. The ESN is embedded within the signal and transmitted each time a cellular call is placed.

In addition to being programmed into the circuitry of the phone's microchip, the ESN typically is found on a label under the cellular phone's battery.

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