Electronic serial numbers (ESNs) were created by the U.S. Federal Communications Commission (FCC) to uniquely identify mobile devices, from the days of AMPS in the United States starting in the early 1980s.
Manufacturer code 0x80 is reserved from assignment and is used instead as an eight-bit prefix for pseudo-ESNs (pESN).
The decimal format separately displays eight bit manufacturer codes in the first three digits, but 14 bit codes are not displayed as separate digits.
As ESNs have essentially run out, a new serial number format, MEID, was created by 3GPP2 and was first implemented by Verizon in 2006.
[2] The last of the previously unused ESN codes were allocated in November 2008.