I saw this as a comment to another post.. I have not tried it but when I read it the steps seems fine. Try at your own risk, but if your phone is already messed up, then the risk is low isn’t it?
I spend a full day trying to recovery my iPhone after upgrading it to 2.2 and finally I was able to go back to 2.1.
So I decided to share it with all impatient morons “like me” in the world; who upgraded their iPhone 3G to 2.2 and lost their unlocked capability; here is the resolution:
1- Download the iPhone 2.1 firmware from: http://www.spaziocellulare.com/ispazio/download-firmwares-iphone-3g/
2- Download QuickPwn21-1 from: http://thepiratebay.org/user/iphonedev/
3- Connect your iphone to your computer and turn it OFF
4- Restart your iphone in recovery by following these steps:
• Connect your iPhone to your computer
• Turn iPhone off
• Hold power and home together for 10 seconds (exactly)
• Release power but keep holding home until the computers beeps (observed on a PC) as a USB device is recognized.
• At no point will the display come on. Now your restore should work.
5- From iTunes; Restore to iPhone firmware 2.1. Hold down “Shift” button and press the Restore button at the same time.
6- Choose the iphone 2.1 firmware you just downloaded in Step 1.
7- Wait till it finish. You will get one of the following errors: 1011, 1013, 1015, you can ignore them.
8- Your iPhone is restored back to Firmware 2.1. Now close iTunes
9- Unlock your iPhone using QuickPwn for iPhone ver 2.1.