If you want to downgrade your phone to a modem firmware of 4.10.01 then you will have to try this procedure which I will be explaining later. Though I recommend you to stay on iOS5 as the untethered jailbreak is about to be officially released. There are some bugs which the Dev-Team is working on and it will definitely be out soon.
Well, first things first. This post is purely educational and does not promise anything. It might work for others but may not work for you.
Okay, i earlier wrote about how to downgrade your phone from iOS 5 to 4.3.3.
iOS 4.3.3 version has a modem firmware of 04.10.01 and iOS 5 has a modem firmware of 4.11.08. to downgrade from the current firmware according to my tech knowledge isn’t possible because once the firmware is upgraded, apple does not sign for any firmware below the current one. But yes i have tried the following steps once on my iPod and it did work, so its always worth giving a shot on the iPhone.
The steps are:
1. Download the 4.3.5 firmware
2. Ensure your hosts file is pointing at Apple. You can do this easily with TinyUmbrella. Simply open it, switch to the advanced tab, UNTICK the option “Set Hosts to Cydia on Exit”, and then exit Tiny Umbrella. DO NOT USE IT FOR ANY OTHER PART OF THE PROCESS!
Alternatively you can edit your hosts file manually if you want to. Ensure you remove all lines which refer to gs.apple.com.
3. Connect your iPhone to your PC and put it into DFU mode.
4. Open iTunes, which will recognise your iPhone in recovery mode, acknowledge the message about this, then press shift-restore (Windows), and select the 4.3.5 firmware you downloaded in step 1.
5. If you followed the instructions, the restore to 4.3.5 should now complete without any errors. When it is complete you will have a stock 4.3.5 iPhone4 again with a downgraded 04.10.01 baseband.
Then you may follow the process to downgrade to 4.3.3 which i wrote in an earlier post.
Now you should be able to go on further (if required) and downgrade 4.3.5 to 4.3.3, ONLY IF you have saved SHSH files for 4.3.3 available. Because your baseband has been downgraded to 04.10.01 you will not end up in a nasty recovery or DFU loop. Remember, there is no way to downgrade further unless you have saved SHSH files saved prior to your upgrade process from 4.3.3 to a higher version.
One more useful piece of information that i would like to share with you is that if you are currently on iOS 4.3.3 and want to upgrade to iOS 5 and work without upgrading your modem firmware then you should download the iOS 5 file and use any application like greenp0ison and cook the update file in the baseband preservation mode so that once you are running iOS 5 on your phone or iPod then you have a baseband of 04.10.01 and not 04.11.08