It goes without saying that Apple doesn’t take kindly to unlocked and jailbroken iPhones. That means those of you running the YellowSn0w unlock will have to hang tight until the Dev Team can craft a custom Firmware bundle of OS 3.0 that won’t brick your iPhone.

Hey, don’t just take our word for it, the Dev Team says on their Blog:

If you find yourself with access to the 3G IPSW for 3.0 via the iPhone Dev Center program, and you are using yellowsn0w, do not update or restore to that official IPSW. You will lose yellowsn0w and find yourself unable to revert the baseband to get it back.
And for those wondering, yes the 3.0 OS is jailbreakable on all devices. It’s just those using 3G yellowsn0w that have to show some restraint and wait for PwnageTool to create a custom IPSW that avoids the baseband update.

While OS 3.0 can still be jailbroken, those trigger fingers will likely corrupt your iPhone’s baseband making it near impossible to revert. Fortunately, a custom version which avoids loading the new Baseband or loading an unlock friendly Baseband will likely be available before 3.0 is officially released.

Via: The iPhone Blog