The MEID was created to replace ESNs, whose virgin form was exhausted in November 2008. As of TIA/EIA/IS-41 Revision D and TIA/EIA/IS-2000 Rev C, the ESN is still a required field in many messages—for compatibility, devices with an MEID can use a pseudo-ESN (pESN), which is a manufacturer code of 0x80 (formerly reserved) followed by the least significant 24 bits of the SHA-1 hash of the MEID. MEIDs are used on CDMA mobile phones. GSM phones do not have ESN or MIN, only an International Mobile Station Equipment Identity (IMEI) number.