This is for people who accidently upgraded their Iphone 3GS New Bootrom to 4.0 and needs to unlock their phone for T-Mobile or jailbreak.
This is a different method than the one ih8sn0w has figured out. I have tested and tried this method on 3 Iphone 3GS New Bootroms so it's guaranteed to work. If you have any questions, please ask and I will help.
This will work for the Iphone 3GS New Bootroom on Version 4.0.
1. You must have an Iphone 3GS New Bootroom on Version 4.0.
2. Must be done on Itunes 9.2.
3. Point Itunes hosts to saurik's server, you DO NOT NEED SHSH BLOBS.
4. Put Iphone in restore mode and restore to 3.1.3 firmware.
5. Error 1015 will occur, and the phone will still be in recovery mode.
6. Run Blackra1n and click make it rain, the phone will go into a black screen for about 20-25 minutes, after that the phone will boot up to the activation screen with version 3.1.3. Blackra1n doesnt jailbreak the phone, it only boots it up after the 1015 error.
7. Now, once you're at the activation screen, redsn0w will not work to hactivate so you will need to use an AT&T sim card to activate.
8. Run spirit to jailbreak the phone.
9. Unlock the phone with ultrasn0w 0.9.3.
I don't think anyone has figured this out yet. I figured it out on accident. And I've tested it on 3 Iphones 3GS with new bootrooms, I hope this helps many of you guys.