MuscleNerd has announced that an upcoming version of RedSn0w will support restoring and allow for downgrade of the iPhone 4S and iPad 2/3 for those with SHSH Blobs saved.
Upcoming redsn0w supports restoring, including iPad2/3 and 4S downgrades (with blobs) http://twitpic.com/9ixsqv ..also stitches on the fly :)
The only caveat so far is that this requires SHSH blobs, meaning your device would have had to have previously been jailbroken on the restored firmware and have run the Cydia package manager on that firmware at least once.
Until the release, A5(X) devices can’t be downgraded with publicly available tools. You can’t use iTunes, because Apple’s authentication servers won’t “okay” old versions of iOS. Older devices such as the iPhone 4 can get their iOS software downgraded with software like RedSn0w, but that the bootroms for A5 devices (and up) haven’t been exploited in such a way as to allow them to be restored to 5.0 (although the less protected iOS 4.3.3 does currently work). Since newer versions of iOS are often found to be incompatible with current jailbreak exploits downgrading allows people who have found themselves “trapped” on a newer firmware which can be jailbroken.
Whatever MuscleNerd’s method is, he’s not using the loophole discovered by iH8sn0w which we reported on in March. Apparently there are legal issues with that particular implementation (likely copyright from proprietary code) and it will not be released.
We will keep you updated!