Users who rely on the jailbreak and unlock are advised not to update directly from iTunes. The full guide and information on how to Jailbreak your iPhone, iPod Touch and iPad follows:
Apple released iOS 4.3 for supported iPhone, iPad and iPod Touches. Current users who rely on Unlock and Jailbreak please do not update directly from iTunes. Since iOS 4.3 is similar to the iOS 4.3GM which was released recently you can use the same method to Jailbreak your device
Tethered Jailbreak
You can use the iOS 4.3GM Jailbreak guide (Windows | Mac) to jailbreak your device in tethered only state. What this means is that you will have to reboot your device in jailbroken state every time you want to access Cydia or any jailbreak related tools. An untethered jailbreak should be available soon, so I would advise you wait for that for an easier solution.
Untethered Jailbreak
No untethered Jailbreak is still available. Stay tuned for one soon
Unlock
At this moment there is no unlock for iPhone 4 users with 2.10.04, 3.10.01 and 4.10.01 basebands.
iPhone 4 users with baseband 1.59.xx please DO NOT update to iOS 4.3 directly. Preserve your baseband and follow the 'Unlocking section' in this guide to unlock your device.
iPhone 3GS users who have used this guide to upgrade to iOS 4.2.1 and use iPad's 06.15.00 baseband can follow the 'Unlock section' in that same guide to unlock your device without your baseband changing.