The notorious Dev Team has posted an entry on its blog warning iPhone jail-breakers (or potential jail-breakers) that the impeding iOS 4.1 update is "a trap" set by Apple.
The post warns that accepting the update is "the surest way to lose your jailbreak and/or unlock".
The post states:
"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".
The post ends with a warning to steer clear from iOS 4.1 until a safe jailbreak procedure that preserves ultrasn0w has been launched.
People that aren't interested in naughty (but not illegal) hacking, should be able to update to iOS 4.1 very soon.