Now, downgrade from iPhone baseband 6.15 will soon be possible as confirmed by the iPhone unlocking expert Musclerd from iPhone Dev Team. He has confirmed via conversation to a user that by Sunday he will be updating redsn0w to downgrade to 6.15 baseband.
@EVILCLOWN2016 I’m aiming for Funday/Sunday for releasing the downgrade from 06.15, but that’s very much subject to possible delay
— MuscleNerd (@MuscleNerd) June 13, 2012
The iPhone 3G / 3GS users will able to unlock their device. The downgrade procedure will be quite simple and there will be an additional option in the redsn0w tool to downgrade from 6.15 BB.
However, there is small possibility of delay in the release but if some issues occur then by next week he will be releasing the downgrade. Musclenerd is also working on the jailbreak of iOS 6. Last week, he has jailbroken iPod touch 4G on iOS 6 but there were many issues like Cydia was broken and many more.