For those who don’t know, previous iPhone 2.0 beta 4 firmware is not pwned. That means unless you are using AT&T or other official carrier with valid developer account, you cannot upgrade iPhone beta 4 firmware with working functions. You will end up with “Activate iPhone” screen.

If you have updated to iPhone beta 4, you will end up to have the “04.05.03_G” modem firmware. It is not easy to downgrade it to 04.04.05_G (Currently we are using at iPhone 1.1.4 official firmware). Since I didn’t obtain iPhone firmware beta 5, I am not sure whether the modem firmware is also “04.05.03_G”.

No matter what it is, if you accidentally upgrade the iPhone to 2.0 beta 4 or 5, you may want to try this. This is the tool to unlock the firmware and enable the phone function again.

After downgrading from the firmware 2.0 beta, the modem will still be 04.05.03_G, launch the Installer, and add “http://s.iphone-forums.de/” as the source. Select the correct tool to unlock the firmware. Try it if you dare.

[via WeiPhone]