Apple has released the iOS 4.3 firmware now and its jailbreak is also available now. The new iOS 4.3 firmware files are exactly similar to the iOS 4.3 GM that was released a week before of its final release and so it could be jailbroken in the same way as we did on iOS 4.3 GM.
You could jailbreak iOS 4.3 on iPhone 3GS (old or new bootrom) and iPhone 4 using the guide given here. Just use the respective PwnageTool Bundles and the iOS 4.3 IPSW files. This method also preserves your baseband so that you could unlock it using the earlier version of Ultrasn0w (Baseband 1.59.xx on iPhone 4 and 06.15.00 iPad baseband on iPhone 3GS).
NOTE: This is a tethered jailbreak, so you should boot your device into a jailbroken state on every reboot(Instructions given).
1. Download the PwnageTool Bundles from here.
3. Download iOS 4.3 IPSW for iPhone 3GS/4.
4. Now follow the steps given here (Except step 7) to jailbreak iPhone 4.3 iOS firmware.
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