Transition from iOS 4.x to iOS 5 and Jailbreaking

I have recently made a transition from iOS 4.x to iOS 5 on my iPhone 3GS and I can say it wasn't a particularly smooth sailing journey. Of course we're talking about jailbreaking it as well. My plan was to do this:

1. Sync & backup iPhone 3GS with iTunes
2. Fully restore iPhone to iOS 5
3. Jailbreak iOS 5 with redsn0w
4. Install AppSync 5.0+ from Cydia
5. Restore from backup to iPhone with iTunes.

Sounds easy right? Wrong! Now usually when after I sync and backup the iPhone before an upgrade of the firmware, I will do a backup of the backup first so I can do it again if I screw it up. I have written an article on how to do this before and you can see it here: [Restoring from a backup for iPhone, jailbreak or not!]

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I was able to do the above steps until step no.5, when it all went haywire. When trying to restore from backup, iTunes gives me an error that says that my backup was either corrupt or it was incompatible with my current iPhone (3GS). It shouldn't be logically incompatible as it was the same iPhone and it shouldn't be corrupt as I didn't touch anything else except for the info.plist file. I tried many times (including restoring the phone again and jailbreaking again) and also from a different computer but to no avail. So it looks like the backup was useless and even the backup of the backup proved futile to the cause.

Fortunately though, I have an iPhone 4 (my main phone now), that has almost identical settings and app on it save for some games' savegames and SMS messages (which I know I'm going to loose). My phonebook was synced with Google so that's not a problem. So what I did next was to sync and backup my iPhone 4, did the same backup of the backup again and modified the info.plist so that I can identify it easily in iTunes. This time though, I used Windows Notepad to modify the info.plist instead of using the Wordpad. I used Wordpad before because it opens the file correctly with all the indentations. With Notepad, its a little messier but I just wondered if using Wordpad screwed up the file.

So after that, I proceed to restore from backup from the iPhone 4's backup to the iPhone 3GS. Lo and behold! It successfully restore from the iPhone 4 backup! It will take a while for the restore depending on how big was your backup. Mine was around 4Gb and that was only data like the pictures, videos and other app settings, it will also have to restore your apps from your iTunes library and those are stored in your iTunes library folder.

A few things to consider when you are trying to upgrade your iOS firmware and jailbreak,

1. Make sure you have synced and backup.
2. Make sure you make a copy of the backup, preferably store it in the different folder.
3. Make sure you have the right iTunes version (iOS 5 needs at least iTunes 10.5)
4. Make sure you have the right redsn0w version. 
5. Make sure you have downloaded the firmware and keep it handy.

If you do not have the right iTunes version, redsn0w will not be able to detect your iPhone in DFU mode, and hence, not be able to jailbreak your iPhone.

So now I have an iPhone 3GS which is jailbroken and it is untethered (it has the old bootrom). Take note that as of writing, only the iPhone 3GS with the old bootrom can have the untethered jailbreak. Other than that, you will have a tethered jailbreak.