Iphone 3GS (ver 4.0) downgrade to 3.1.2

[tcella]

Hello There anyone,
I am trying to restore clean image on my iphone and downgrade it at the same time in preparation for jail breaking it for resell (I have an iphone 4 now).
I have followed many different instructions that are out there in many different forums.
All of them fail when I get the phone into DFU mode and do the option update from my mac in itunes and point to my image file. I get a message "The iphone "Iphone" could not be restored because the firmeware file is not compatible"

I'm stumped. I download the file from here...
http://appldnld.apple.com.edgesuite....1_Restore.ipsw

Any one can help me out if you wish..

Thanks,

[i.Annie]

If you don't have your SHSH blobs saved, you can't restore/downgrade.

[iPhoenix3g]

That firmware/restore file is already here in the downloads section.

[i.Annie]

Regardless of where the file is, a restore cant be done without SHSH blobs. Im sure the firmware is not the problem.