Restoring your iPhone 3G to OS 3.1.3
I had to restore it back to 3.1.3.
spicyj gave me the starting point here:
http://news.ycombinator.com/item?id=1453553
I ran into a few problems, here is how I got it to work:
1) Download 3.1.3 firmware for iPhone 3G from http://www.felixbruns.de/iPod/firmware/.
2) You have to put your phone in the appropriate DFU mode for downgrades. (Whatever DFU stands for).
Switch of your iPhone, connect the USB cable to your mac / PC and put it in DFU mode with following instructions - Click the Home + Power On button for 10 seconds exactly - Release the power button and continue to click on Home. The display should never turn on, but your iTunes should recognize the phone and warn you about recovery mode.
3) Option click the restore button and choose the 3.1.3 firmware you downloaded. Let it perform the recovery.
4) If it fails with an error 1015, click ok. The firmware is restored, but you have to snap the phone out of the recovery mode now.
5) Download iRecovery as explained in this link.
http://www.ihackintosh.com/2009/09/recover-iphone-3gs-from-apple-logo-or-recovery-mode-loop/
6) As explained there, copy the libusb-0.1.4.dylib to /usr/local/lib and give it executable permissions.
7) Run ./iRecovery -s from the extracted directory.
8) Set autoboot to true inside the iRecovery console:
setenv auto-boot
saveenvs
fsboot
9) I had to do fsboot thrice and nothing happened. It should have rebooted by now.
I did a power down and restarted the iPhone, and it was back up on 3.1.3 firmware.
If you run into problems or your phone is stuck in the recovery icon mode (USB port meets iTunes icon), please check out iRecovery and read all the possibilities there (there is a reboot command which might work, I didn't try it).
The downside to this is since my last iPhone backup was with iOS4, I could not restore it, I had to setup my phone as new. That is something I can live with.
Upside - the phone seems MUCH faster now ;).