Unlock

This is the process by which the iPhone baseband is modified to accept the SIM card of any GSM carrier. This is entirely different than a Jailbreak.

Official Unlock

At +0x400 in the seczone, a token is stored encrypted with the NCK. Apple, knowing the NCK, sends it using an activation token over iTunes. The phone receives an AT+CLCK="PN",0,"......NCK......" It decrypts the token with the generated key. If that decryption, after dersaing with Key 2, is a valid token for the phone, it is stored back to that flash with the token TEA, but not RSA decrypted. On startup, if the lockstate table says the phone is unlocked, it validates that RSA token.

Old AnySim Patch (1.0.X)

This patch disabled signature checks. So the RSA signature would always validate, and the phone would always appear to be unlocked and every NCK would appear to be valid. This patch made inadvertent changes to the seczone which disabled the baseband upon attempted upgrade. The virginizer was written in response to the corruption this caused, and allowed users to overwrite the corrupted seczones.

New AnySIM Patch (1.2+)

This patch, also know as the ignore MCC/MNC patch, makes every MCC/MNC pair appear valid. This patch is overwritten on a reflash of the baseband, and doesn't touch the seczone at all. It must be reapplied for every baseband upgrade to maintain the unlock.

IPSF

See IPSF for main article. This patch changed the lockstate table to read unlocked and created a spoofed RSA token that was seen as valid by BL3.9. It overwrote your previous token, which means the phone could nor longer be officially unlocked, unless a restore of the token was performed from a previously made backup. Since the token isn't modified in a baseband flash, this unlock survived a baseband downgrade or upgrade. Apple attempted to combat this by requiring AT+CLCK command to be sent every startup. In a officially unlocked iPhones, lockdownd does this. In a late verion IPSF phone, signal.app does this.

Cloning Officially Unlocked Phones

This has been suggested by many people, however it has been well investigated and virtually ruled out for the following reasons. Replacing the baseband's bootloader or firmware of a locked phone with that of an officially unlocked phone does not unlock the phone, as the unlock information resides in a different flash area of the baseband and is unique to each phone. Copying the seczone would duplicate IMEIs which in turn would result in a ban of these. Moreover, these cloned phones would not even be unlocked by the NCKs of the phone they were cloned from as the HWID and NORID is concatenated with the NCK to produce the decryption key used on the RSA seczone token.