If you want the short answer scroll to the bottom.
BACKSTORY
I had a Iphone 3GS with the newer boot rom and jailbroken on 3.1.3. I decided that I wanted to upgreade to 4.0.2 and jailbreak it again but alas as of this post there is no jailbreak for 4.0.2. So I upgraded to 4.0.2 anyways via Itunes. I then discovered that you can downgrade your iphone to 3.1.3 or 4.0 or 4.0.1 IF AND ONLY IF you saved your shsh blobs via Cydia, thankfully I had, so this is what I did.
THE PROCESS
So I followed koi2881's guide to downgrading from 4.0.2 on youtube. I downloaded Tiny Umbrealla and the firmware.
Tiny Umbrella makes it so that iTunes communicates with the Cydia SHSH server and not the itunes server (it can also download your shsh blobs from Cydia) and the firmware is the software package you want to downgrade to, 3.1.3, 4.0., 4.1..etc.
PROBLEM 1
When I "Shift-Clicked" the restore button and I didn't see the firmware in the folder I downloaded it to, I had to rename the zip files to .IPSW instead of .ZIP, problem solved.
PROBLEM 2
When I opened the firmware I wanted to load via itunes, it said, "The iPhone "iPhone" could not be restored. An Unknown error occured (3014)." It seems to me that Tiny Umbrella was not doing its job. I looked at the host file located at "C:\windows\systems32\drivers\etc" and at the bottome I saw "127.0.0.1 gs.apple.com". It appears to me that apple was being redirected to my host computer and that's not correct. So after reading Suariks page on shsh blobs, i correctly changed the host file to say "74.208.10.249 gs.apple.com". Problem solved, this also eliminated the need for Tiny Umbrella.
PROBLEM 3
This time after selecting the firmware package to open, it said, "Error 3014". I turns out i put a # mark in front of the ip address in the host file, dont do that, that's bad. Removed # mark and all is well.
After that everything went smoothly.
SHORT ANSWER:
- Open notepad as administrator
- Select File open and go to: C:\windows\system32\drivers\etc\host
- insert the following at the bottom of the file: 74.208.10.249 gs.apple.com
- start iphone in restore mode (turn if off and hold the circle button).
- Open Itunes and shift click "restore"
- Select the firmware version you want to downgrade to
- After the firmware upgrade you'll all your stuff unless you restore a backup.
- if you want to jailbreak go to jailbreakme.com from you iphone
