updated 01:55 pm EST, Mon December 5, 2011
iPhone 4S not yet supported
An updated Windows utility, iFaith, promises to let iPhone owners to downgrade to earlier versions of iOS 5, according to famous iOS hacker iH8snow. With the advent of iOS 5, Apple changed the code in such as a way as to prevent normal downgrading methods. iH8snow says he has discovered a way around the obstacle, enabling dumped iOS 5 SHSH blobs to accept unsigned restores.
The technology may be essential for jailbreakers, as hackers MuscleNerd and pod2g have noted that the first untethered jailbreak for iOS 5 will require v5.0. The current official release of iOS is v5.0.1, and Apple is already at work on iOS 5.1.
Some limitations still exist with iFaith. It must for instance be used in tandem with the redsn0w jailbreaking utilty, not sn0wbreeze. It also doesn't support devices equipped with A5 processors, namely the iPhone 4S and the iPad 2.