Like most firmware updates… iOS 4.1 breaks the current jailbreak and unlock. This is especially true for unlockers due to the fact there there is no way to revert your baseband. I’m sure the guys over at the Dev-Team are working on updating the jailbreak. We will keep you informed on how they are doing. Below is what the Dev-Team has to say about upgrading to iOS 4.1.
This time of year there are lots of new iPhone owners, and not everybody knows that accepting new iOS updates is the surest way to lose your jailbreak and/or unlock. While those of you who have Cydia or TinyUmbrella backups of your FW hashes will always be able to get back to 4.0.1 if you make this mistake, this doesn’t hold for unlockers. There’s currently no known way to revert your baseband — if you update your baseband you’ll lose the ultrasn0w unlock, possible forever.
Please stay away from this 4.1 release until a safe jailbreak procedure (which also preserves ultrasn0w) is developed and released.
P.S. There are a tiny number of iPhone3G owners who can revert their basebands due to a flaw in very early bootloaders…you will already know if you fit in this category!
Head over to the Dev-Team’s blog for more info.