The electronic serial number, or ESN, of a mobile phone is printed either on the device or on the box that it came in, or it can be looked up using the device itself. ESNs are sets of numbers used to identify all mobile phones in the United States, and they are assigned to the devices by manufacturers.
The locations of ESNs vary according to the brand of the device. On some mobile devices, the ESN can be found by removing the battery and checking the print on the sticker beneath the battery. The ESN is usually indicated by the abbreviation S/N. In other cases, the ESN is located on the outside of the box of the device, usually in the form of a sticker with bar codes. ESNs may also be looked up using the device, but the process varies according to the device model and brand.