But still, many users accidentally upgraded to iOS 4.1 and lost their jailbreak/unlock making their iPhone/iPod Touch virtually unusable. If you don’t rely on unlock & have accidentally updated to iOS 4.1 then below is guide to downgrade to iOS 4.0.2/4.0.1 or 4.0 which can still be jailbroken using JailbreakMe.com Note: The below method works on iPhone 4, iPhone 3GS & iPhone 3G only if you have backed up SHSH Blobs.
How to Downgrade iOS 4.1 on iPhone 4, iPhone 3GS & iPhone 3G
Download TinyUmbrella in order to download your SHSH blobs saved on Saurik’s server
Connect your iPhone and run TinyUmbrella. Look for “Advanced Options” and under ‘Device/Version’ drop down list, select iOS 4.0.1
select “Cydia” under “Request From”. Then hit “Save My SHSH”. This will grab your SHSH files from Saurik’s servers and save them to your PC.
Now download iOS 4.0.1
Put your iPhone in DFU Mode (To do so, launch iTunes and plug your iPhone in. Press and hold the Home and Power button together for 10 seconds. After 10 seconds, release the Power button while still holding the Home button until iTunes pops up and says it has found an iPhone in recovery Mode.)
Run TinyUmbrella and click the “Display SHSHs” button to make sure your SHSH blobs were downloaded to your computer. Once done, click “Start TSS Server”.
Restore your iPhone via iTunes. Hold Shift key (Win) or Alt key (Mac) while clicking on restore button. A window will open. Simply select the firmware you downloaded in step 4.
Your iPhone will be downgraded/restored to the iOS version you chose. iTunes might give you error messages (error 1011, 1013, and 1015). Don’t worry about them.
We now need to get your iPhone out of recovery mode. To do so, open TinyUmbrella and click “Kick Device Out of Recovery”. We need to stress again that above method only lets you to downgrade iOS but can’t downgrade baseband version. IMPORTANT: If you see this message in your console “Could not start TSS service on port 80 because you have something running on that port already!” Then TinyUmbrella cannot protect you! You must kill skype or teamviewer or whatever app is running and using port 80. [via]Blogsdna
