The iPhone Dev Team has released some instructions for re-jailbreak to the iPhone 3GS users who has been accidentally upgrade their devices to iPhone OS 3.1. As some of iPhone 3GS users after getting update to OS 3.1 (which was not recommended by Dev Team) claimed that now this is not possible for them to downgrade the devices to iPhone OS 3.0 or OS 3.0.1 because of Apple’s restrictions.

Here are the instructions by iPhone Dev Team for the users of iPhone 3GS who accidentally upgrade to iPhone OS 3.1:

“If you want to come back to the world of the jailbreak (but NOT the sim unlock, sorry!) then saurik’s new “on file” server may be able to help.  He’s got all the details in a new article so do check it out.”

Even if you did not update your 3GS to official 3.1 (good job!  You really shouldn’t do that!), then you should still read the article and make those changes today.  We fully recommend redirecting your iTunes signing process through saurik’s “on file” server to future-proof your 3GS jailbreak through all future updates.

AFTER ADJUSTING YOUR ITUNES SETUP, YOU SHOULD STILL AVOID DOING AN ACTUAL FIRMWARE UPDATE. For all the reasons mentioned in this post, you’ll lose the unlock forever, and lose the jailbreak until a new one for 3.1 comes out.  And there’s no guarantee that your 3.0 signed files were captured by saurik in time.  This is more about protecting your 3GS jailbreak in future updates — it’s not a way to jailbreak 3.1 right now.

The iPhone Dev Team also provides some instructions for the users who don’t upgrad their devices  to iPhone OS 3.1:

NOTE #1:

The carrier sim unlock is a different story.  Jailbreaking and unlocking have two different security mechanisms, and if you update your 3GS (or 3G) to 3.1, you will lose your carrier unlock, possibly forever.  Even if you downgrade from 3.1 to 3.0, you will have lost your carrier unlock.  So if you think you’ll ever want to carrier unlock your 3G or 3GS (or maybe give it away or resell it later as an unlockable iPhone), then please stay clear of all official Apple IPSWs.  You’ll soon be able to create custom 3.1 IPSWs using PwnageTool that let you pre-hack your 3.1 update in a way that preserves the carrier unlock.

NOTE #2:

The custom IPSW flow using PwnageTool also ensures that even if Apple fixes all the iBoot holes, you’ll still be able to retain your jailbreak through later updates.  That’s because a jailbroken iPhone will happily accept a custom (pre-jailbroken) firmware update even though it’s not blessed with Apples signatures.  This is the “once jailbroken, always jailbroken” approach.  It’s very powerful, but it requires you to only update to pre-hacked IPSWs.

NOTE #3:

None of this applies if you have an iPhone 2G, iPod touch 1G, or iPod touch 2G.  The iPhone 3G is also unaffected by Apple’s signing process for the jailbreak, but it is susceptible to permanent loss of the carrier unlock as mentioned in note #1.