Finally, after wait of several months, Devteam has finally updated their classical tool called Redsn0w to support downgrading. We all know that downgrading of A4 devices have been possible from quite sometime, but now you can downgrade newer devices as well. These devices include iPhone 4S, iPad 2 and iPad 3 using the latest update of Redsn0w. Please note that those who had saved SHSH Blobs either using TinyUmbrella, Cydia or Redsn0w would be able to downgrade their A5 based devices.
If you are willing to fetch the SHSH Blobs now for the older firmware, it’s actually not possible. Because Apple has closed the signing window already. If you had saved SHSH Blobs using TinyUmbrella and want to downgrade your iPhone or iPad using latest Redsn0w, TinyUmbrella has a button which can show you your blobs. Just point Redsn0w to those SHSH Blobs for the downgrading process to proceed.
It’s also interesting to note that this downgrade process first update your iDevice to the latest firmware and then downgrades to iOS 5.0.1/iOS 5.0. Hence, if you rely on a software unlock like ultrasn0w, do not use this process. The baseband of your iPhone would be updated, due to which you would lose the unlock. However, if you have been using SAM method to unlock iPhone 4S for a specific SIM, you should not bother about it at all. You could still unlock after the downgrading process is completed.
There are few devices which haven’t been tested on the firmware yet such as iPad 3,2 and iPad 2,3. If you want to test the latest Redsn0w on these devices, you could give it a shot. And if you are successful, do inform the DevTeam on twitter or comment section of their blog. Apple can close this downgrading in upcoming software update. However, it is not known why they haven’t done it yet. This update of Redsn0w includes a bunch of new code, so you should stick to old Redsn0w if you don’t need the new functionality.
You can know about the progress of iOS 5.1 untethered JailBreak from here.