Firmware Downgrading

For those unlucky enough to have "accidentally" upgraded their iPhones to firmware version 3.1.3 ( or received a new iPhone with that version firmware ) ... if you are looking to downgrade your firmware to, say 3.1.2, hoping that you can unlock your iPhone, sorry, no can do.

With the exception of the 2G, which can always be unlocked, once you upgrade your firmware, the component that is responsible for the unlock, the baseband, is permanently upgraded. This means that even if you downgrade your firmware, the baseband version stays the same. So, for example, if your iPhone was running 3.1.2 firmware and was jailbroken and unlocked, then you upgraded to 3.1.3, losing your jailbreak and unlock, you cannot downgrade your firmware to 3.1.2 and expect to be able to unlock with blacksn0w, it just won't work.

Those in this situation will simply have to wait until the next unlock is developed. DO NOT hold out hope that there will be an unlock developed for the baseband that comes with 3.1.3 ... it probably won't happen. The jailbreaking community in general believes that the next unlock will be developed for the next firmware release, probably 3.2 or 4.0.

The ONLY hope that I hold out is to the 3G owners. If you have a REALLY old 3G, manufactured in 2008, there is a hope that your baseband can be downgraded. Look at your serial number, Settings -> General -> About -> Serial Number.

If the third digit is 8 ( that means that it was manufactured in 2008 ) and the next two less than 36 ( meaning the week that it was manufactured ) then you have a good chance of downgrading your baseband to an unlockable version using the very solid ultrasn0w unlock.

For everyone else, the waiting game continues.