Can you restore a phone with an old version of iOS if that phone was never upgraded? I have a couple of iPhones running iOS 4 that I want to do a restore on. These phones have never been jailbroken, and I'm using the .ipsw that is the exact same version that's currently on the phone:

iPhone 4 - 4.3.5 (8L1)

iPhone 3GS - 4.3.2 (8H7)

When I try to restore from the .ipsw in Windows 7, I get the error:

The iPhone "myphone" could not be restored. An unknown error occurred (3194).


This error means that I need to upgrade iTunes, but I'm running the latest version. Also, I'm able to restore my other iPhone 4 using 5.0.1 just fine.

When I try to do the same on my Mac, I get the error:

The iPhone "myphone" could not be restored. The device isn't eligible for the requested build.


When I click "More Information" I see that it's also error 3194.

I checked in WireShark, and I do get a TCP connection with apple just before the error. It's encrypted though, so I have no idea what it sends/receives, but I can confirm that there's two-way communication. I tried the restore both over my company's connection, and my 3G connection just to make sure it didn't have anything to do with the IP address I was using. Also, I verified that the phones are authorized for that iTunes installation.

Any ideas?
The official answer to this is no, you can not restore to a previous version of iOS other than the current one available from Apple. This is because iTunes is attempting to obtain tokens from the Apple signing servers to authorize the device when restoring.

The non official answer is yes, but requires some technical skills using iFaith. Post back if you require assistance down this path.