After releasing iOS 4.1 beta to developers, Apple has now rolled out iOS 4.0.1 to the general public which uses the new formula so that signal strength is reported more accurately. It’s compatible with the iPhone 4, iPhone 3G S and iPhone 3G, but apart from that, there’s nothing else new this minor iOS firmware update has to offer.
With that being said, jailbreak aficionados out there have nothing to worry about as it’s been confirmed that iOS 4.0.1 can be hacked. In fact, redsn0w 0.9.5b5-5 which can jailbreak iOS 4.1 beta has been proven to work just fine on the iPhone 3G with iOS 4.0.1 installed.
Other iPhone models, unfortunately, will have to wait for the other jailbreak tools to be updated so that they'll be compatible with this latest iOS firmware. For your unlocking needs, ultrasn0w 0.93 will suffice as the baseband likewise wasn’t changed in iOS 4.0.1.