IMEI is explained here

The following codes work with most mobile handsets.

International Mobile Equipment Identity (IMEI)
Type the following:- *#06#
You should receive the following information : -

XXXXXX–XX–XXXXXX–X

TAC——-FAC——-SNR—-SP

TAC = Type Approval Code
FAC = Final assembly code
SNR = Serial number
SP = Spare

Every GSM mobile has an unique International Mobile Equipment Identity (IMEI), which is used to identify the mobile phone but not the network subscriber using the phone. In order to maintain the independent identities of the GSM mobile phone and the GSM subscriber, the international mobile equipment identity (IMEI) is completely independent of the international mobile subscriber identity (IMSI) Each GSM network operator maintains three lists of international mobile equipment identities (IMEIs) in its equipment identity register (EIR):

GREY - GSM mobile phones to be tracked, BLACK - barred GSM mobile phones, perhaps those that have been stolen and WHITE valid GSM mobile phones.

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