Apple Updates iPhone baseband with iPhone 3.1 firmware – STAY AWAY from this Update
This fact cannot stressed enough! Every time people are warned about updates from Apple disabling Jailbreak / Unlock , some people still end up accidentally updating via iTunes. Why take a chance while you can get the new iPhone firmware goodness with a few days wait?
Launch iTunes, Click on Preferences – > Under General Tab Uncheck ‘Check for new software updates automatically‘. Wait for a confirmed jailbreak and unlock for the newly released firmware and then update.