Shortly after unofficial version, we have PwnageTool Bundle 4.3 from msft.guy to jailbreak iOS 4.3 Beta 1. So, all users developers who updated to iOS 4.3 Beta, can get a taste of Cydia on iOS 4.3. Here is the guide:

WARNING: This guide requires you to unofficially patch the PwnageTool with 4.3 bundles from msft.guy. It, however, is not recommended for use if you’re not a developer/advanced user. Continue at your own risk, good luck!

First, download the bundle: Bundles_iphone4_4.3b1.zip

Then, follow the instructions:

• Unpack the original ramdisk: xpwntool orig_restore_rd.dmg restore_rd.dec.dmg -iv .. -k .. (use the keys from wiki)
• Mount the ramdisk: hdiutil attach restore_rd.dec.dmg
• Free up some space: rm /Volumes/ramdisk/(some unneeded large-ish file)
• Patch asr: mv /Volumes/ramdisk/usr/sbin/asr /tmp/; bspatch /tmp/asr /Volumes/ramdisk/usr/sbin/asr (bundle_path)/asr.patch
• Change the restore options: edit /Volumes/ramdisk/usr/local/share/restore/options.plist with Property List Editor, add ‘UpdateBaseband’ = false – see http://theiphonewiki.com/wiki/index.php?title=Preventing_Baseband_Update for details
• Unmount the ramdisk: hdiutil detach /Volumes/ramdisk
• Re-encrypt the ramdisk: xpwntool restore_rd.dec.dmg pwned_restore_rd.dmg -t orig_restore_rd.dmg -iv .. -k ..
• Replace the ramdisk inside of CFW produced by the Pwnage Tool with pwned_restore_rd.dmg You can either unzip and re-zip the CFW or replace it inside of /tmp/ipsw dir when PwnageTool is running.

From msftguy’s GitHub