WARNING: To my knowledge anything that happens will be an improvement yet I am not responsible for any damage done to your iPhone while using this tutorial.
Hold the power and home button for about 10 seconds. Then release the Power button while keeping the Home button held until the screen stays black. Repeat until desired result. You are now in DFU mode.
Plug your phone in the computer and wait for iTunes to recognize it in recovery.
Press the Shift key (on Windows) or alt-option key (on Mac) and click Restore.
Now find the downloaded IPSW and click on it. Wait for iTunes to do the rest.
Yay! Your iPhone should now be booting up. Now follow this tutorial to learn how to downgrade from iOS beta 7 to 4.3.3
If you have any questions feel free to comment or shoot me an e-mail. Hope this works:)
Once all these files are downloaded (or installed) we can begin.
WARNING: I am not responsible for any damage done to your phone due to unforeseen and uncalled for side-effects and results. Proceed at your own risk.
First of all make sure your iPhone is running 5.0 beta 7 with the iPad baseband 06.15.00. Open up Tiny Umbrella (Wait for it to load) and click on “Start TSS Server”. Now open up Snowbreeze (or Pwnagetool) and follow the instructions to create a custom 4.3.3 IPSW. Now put your iPhone in DFU mode by following the on-screen instructions.
Now iTunes should now open-up telling you that it has discovered an iPhone in recovery mode. (Tiny Umbrella should still be open running the TSS Server). Click on Restore while holding the shift key (on Windows) and alt-option key (on Mac). Find the custom 4.3.3 ipsw you created (usually on desktop) and click on it. Now don’t do anything rash and wait for iTunes to restore your Phone.
Now your iPhone should boot-up in recovery mode (black screen) and the same message about iTunes finding an iPhone in recovery mode… Ignore it and now launch Tiny Umbrella, stop TSS server and click on “Fix Recovery”. After about a minute your screen should now have something about Greenpois0n. Hold the Power and Home button until the screen goes black then release both buttons.
Now launch Redsn0w and point it to the original 4.3.3 IPSW (the one from Apple). After the verification process, uncheck install Cydia and just click on install iPad baseband. Now click finish, and wait for the process to finish.
Now relaunch Redsn0w and this time check install Cydia. Wait for process to finish. Now we are almost done
Launch Cydia on your iPhone 3GS and install Ultrasn0w.
And voila! There you have it:) A downgraded fully working iPhone 3GS running 4.3.3! Feel free to comment, contact me or ask any questions:)