That being said, for those with older A4 devices, it is possible to enjoy a tethered jailbreak on iOS 5.1 and still downgrade back to previous firmwares if you have your SHSH blobs for those firmwares.
With A5 devices like the iPad 2, and the iPhone 4S, it is impossible at the moment to downgrade to any older iOS 5.x firmware, even if you have your SHSH blobs saved. So don’t upgrade to 5.1, especially if you care about your iPhone 4S jailbreak.
If you have an iPhone 4, iPod touch, iPhone 3GS, or original iPad, then check inside for a tutorial on how to perform a tethered jailbreak on iOS 5.1…
Step 1: Download RedSn0w 0.9.10b6 from our downloads page and run it.
Step 2: Place your iPhone 4, or iPod touch, etc. into DFU mode.
Step 3: Click jailbreak on RedSnow, and it will go through the process of finding the necessary firmware. It will then ask you to install Cydia, make sure that is selected and click next.
Step 4: You should see a lot of scrolling text on your device, and eventually you will be back to your Home screen. You will see a Cydia icon but it will be white. That is because you have to perform a tethered boot.
Step 5: Place your iPhone 4, or iPod touch, etc. back into DFU mode.
Step 6: Click back on redSn0w and select Just boot. This will perform a tethered boot, and once your device returns to its Home screen, you will see a usable Cydia app icon. Open Cydia, and enjoy your jailbreak.
Note: Each time you reboot your device, you will have to perform steps 5 and 6 again to perform a tethered boot.
Again, we can’t stress enough how important it is to stay away from iOS 5.1 if you care at all about your iPhone 4S jailbreak. iPad 2 owners will also be impacted, so don’t update either, though, you can still downgrade to older 4.x firmware if you have your blobs for iOS 4.x.
Are you going to jailbreak your iPhone 4, iPod touch (4th generation), etc?