UPDATE #2: AT&T iPhone can be factory unlocked on any iOS or baseband. Unlock it now.
UPDATE #1: Use Turbo SIM to unlock your iPhone 4 now.
It sure is busy with the iPhone Dev Team as we just found out that besides them working on a fix for the GPS issue, 6.15.00 baseband downgrader, new Greenpois0n for untethered iOS 4.2.1 jailbreak and the unlock for iPhone 4 with basebands 2.10.04 or 3.10.01; apparently they may also be working on a baseband downgrader for iPhone 4!
It has not been revealed how the tool would work but most likely it would be something like Fuzzyband; which was developed to downgrade iPhone 3G baseband with old bootloader. iPhone 4 has basebands 2.10.04 and 3.10.01 – both cannot be unlocked yet. The only iPhone 4 baseband which has been unlocked is version 1.59.00.
Speculatively speaking, this is probably just a concept for now as mentioned by @MuscleNerd on this Tweet reply to a user:
@mfaizulislam: for Baseband downgrade, can it be applied to iPh4 ?
@MuscleNerd: conceptually, yep probably. But new i4 unlock must precede that because otherwise, nothing to downgrade from 01.59 to
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