After literally spending days trying to get my O2-locked UK Streak back to 1.6 (my AT&T Streak is staying at 2.1), however, I can say that it was pretty much the opposite for me. Although many people have been able to get back to 1.6 with no problems doing the same things I tried, I just couldn't. I tried every single thing "verified" to work by people in forums and downloaded countless versions of recovery images and ROMs from various sources, but nothing worked.
I was actually just about to give up and write a post about how I wouldn't be able to cover anything specific to 1.6 on the site because I didn't have access to a 1.6-running Streak. Then it dawned on me that maybe instead of following other people's "proven" steps to revert to 1.6, I should pick and choose certain instructions and just combine the methods described. I had already followed the directions to a T without success before, so I didn't have anything to lose.
And oh my god, it worked!
Here's how to do exactly what I did:
- Download this recovery image discovered by marciu at MoDaCo.
- Extract it using something like WinRAR if you don't already have a program that can recognize RAR files. You can extract it anywhere, but it's easier to leave it on the desktop.
- Download this Dell ROM (build 4399).
- Rename the ROM Update.pkg and move it to the root directory on the Streak's microSD card.
- Turn off your Dell Streak and put it in bootloader mode.
- Press the fastboot button in the top-right corner, wait about 10 seconds, and connect the Streak to your computer. You should see "fastboot_mode" on the Streak's screen.
- Open a command prompt on your computer. In Windows, you can do this by typing cmd in the Start Menu's search bar and hitting Enter.
- Navigate to the recovery folder by using the cd command. If you extracted the contents to your desktop and left everything as is, you should be here: C:UsersYourNameHereDesktoprecoveryrecovery
- Now type fastboot flash recovery recovery.stock.new.img and hit Enter.
- Within seconds, you should see "Download RECOVERY Done!" on the Streak.
- Now remove the Streak's battery and put it back in.
- Hold down both volume buttons while pressing the power button.
- Select option 2 from the menu.
- Cross your fingers that it worked. When the Streak reboots, you should see the 1.6 lock screen.
What made this work for me is using fastboot to flash this particular recovery image. My Streak simply would not cooperate with any other combination of files or methods (original stock recovery image, several versions of clockwork recovery, rooted 1.6 ROM, .bat files, ROM Manager, update.zip, etc).
I don't know why things that others had success with didn't work for me, but sometimes gadgets have their own minds and will do what they want to do.
So if you've tried everything else you've seen in forums and still can't go from 2.1 to 1.6, then give this a try. Maybe it'll work for you too.