mei4dIMEI, MEID, and ESN numbers can be used to track mobile devices for the purposes of repair and replacement as well. If a device is being repaired or replaced, the manufacturer or repair center may use the device’sOn the following devices, find the serial number in Settings and the IMEIMEID (the MEID is the first 14 dits of the IMEI) on the back: iPhone 6. iPhone 6 Plus. iPhone SE