So, you got your hands on iPhone OS 4.0 Beta but want to give it back because many of your favorite iPhone Apps don’t function correctly as they were written for iPhone OS 3.x?
Read on and I’ll point you to an excellent step-by-step tutorial on how to downgrade to version 3.1.3 of the iPhone 3GS firmware.
At the time of this post, despite much misinformation on the web, you can only downgrade from 4.0 Beta to a previous version of the iPhone firmware on a Macintosh or a PC with a virtual machine running the Mac OS.
While you can only perform the actual downgrade on a Mac, you may perform the final step listed in the tutorial on your Windows PC should you use it as your primary iTunes host. Doing this will allow you to put your iPhone back to the way it was before you upgraded to OS 4.0 Beta, assuming that you made a backup of the iPhone before upgrading.
So, for example, if a friend of mine had somehow managed to get her hands on OS 4.0 Beta but wanted to downgrade and assuming she only had a Windows PC, she could bring her iPhone to me and I would perform all but the final step on my Mac. That is to say, I would power off her phone as described in the tutorial and return the iPhone to her. I would caution her not to power on her iPhone until she was ready to connect it to her Windows PC where iTunes would reactivate and complete the restoration process.
Yes! Yes! Yes! I realize that she would most likely never have been able to upgrade to OS 4.0 Beta, in the first place, unless she had access to a Mac but, as with many things in life, that is not the point! (Big Smile)
Remember, proceed at your own risk.
Good Luck and I’ll See You On The Down Side.