With this method you can downgrade, unlock(only iPhone first generation), activate and jailbrake iPhone 2G. This method has been extensively tested and proven to work 100% only on a first generation iPhone(2G). It is not known if a 3G iPhone can be downgraded and jailbroken using the same method. If any of you succeed to downgrade a iPhone 3G, please post a comment so we can help other people with buggy firmware. Thanks.

I’d like to inform you that the whole process was executed on a Windows XP machine. I heard that it doesn’t work every time on Vista. Mac users(I love Mac myself) please borrow an XP machine if you have to. As I said, it is proven that this process will work only if executed on a Win XP machine.
Before you begin, download everything you’ll need:
- Install/Update iTunes to latest version 7.7.1(only the latest iTunes version can restore firmware image from 2.0.1 and 2.0.0)
- Download iPhone first generation restore firmware image version 2.0.0
- Download latest version of Winpwn tool
- Download both 3.9 and 4.6 bootloaders
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here.