Apple's iOS 4 looks great, has loads of new features, works just fine on a 3GS. But it's turned our iPhone 3Gs into expensive ornaments: it made them - and the 3Gs of everyone we know - so slow they were barely useable.

The good news is that you can fix it; the bad news is that you need to dump iOS 4 and it takes ages. Here's how to roll back iPhone OS to 3.13.

Disclaimer: Future Publishing Limited provides the information for this project in good faith and makes no representations as to its completeness or accuracy. Individuals carrying out the instructions in this project do so at their own risk.

Step 1

Before you do anything, sync your iPhone with iTunes and ensure anything you want to keep - including contacts and photos - is on your computer. If you've disabled syncing of contacts, photos and so on it might be an idea to enable them again and do another sync.

We can't stress this enough: the downgrade will wipe your iPhone, and once you're back on OS 3.1.3 you can't restore data from backups made in iOS 4.0 or 4.0.1. That means if something hasn't been copied from your iPhone to your computer and you've added it since upgrading to 4.0 or 4.0.1, you'll lose it permanently.

Downgrade iphone 3g firmware

Step 2

Now, we need to find iPhone OS 3.1.3. This should be on your computer: on a Mac, go to your hard disk and open up Macintosh HD > Users > Yourname > Library > iTunes > iPhone Software Updates; on a PC, head for C:\Documents and Setting\Yourname\Application Data\Apple Computer\iTunes\iPhone Software Updates. The one we're looking for is iPhone1,2_3.1.3_7E18_Restore.ipsw. If it isn't there, download it.

Please note this file is for a 3G, not a 3GS: if you're downgrading one of them for whatever reason, the .ipsw file you need starts iPhone2,1.

Downgrade iphone 3g firmware

Step 3

Time for another download: RecBoot. On Windows, you'll also need to make sure you've got .NET 4.0 installed, and if you're running Vista or Windows 7 you'll need to run it in Compatibility Mode. Full instructions are here.

Now, put your iPhone into recovery mode. To do that, connect your iPhone to your computer and switch it off. When it's completely off, press and hold the power button and the Home button for ten seconds and then let go of the power button. Keep pressing Home until iTunes says that it "has detected an iPhone in recovery mode".

Downgrade iphone 3g firmware

Step 4

If iTunes hasn't done it already, select your iPhone in the left hand iTunes panel so the Restore button is visible. Don't just click it, though: Alt/Option-Click it if you're on a Mac and Shift-Click it if you're on a PC. This enables you to select the file to restore from, which is the .ipsw one we looked for earlier, so locate that, select it and click on Choose.

Downgrade iphone 3g firmware

Step 5

iTunes will now give you a factory-fresh iPhone 3G running OS 3.1.3. The process takes ten minutes or so, and when it's finished iTunes will probably tell you that the iPhone couldn't be restored because of an unknown error. Don't worry about this: that's why we downloaded RecBoot. On a Mac, run the RecBoot Exit Only application; on PC, launch RecBoot. Now, select Exit Recovery Mode.

Downgrade iphone 3g firmware

Step 6

Your iPhone should now restart, and after a moment iTunes will ask whether you want to set it up as a new iPhone or restore from a backup. Now that you've downgraded you can't restore from iOS 4.0 or 4.0.1 backups, so you'll have to choose a pre-iOS 4 backup (if you have one). The restore process takes about ten minutes.

Downgrade iphone 3g firmware

Step 7

Your iPhone should restart again, but it's not ready to use yet: now, you need to sync it. That means copying across all your music, all your movies, all your apps… this would be a good time to make dinner, start a family, make a volcano from mashed potato or write the Great American Novel. Depending on how much stuff there is to sync, syncing your newly restored 3G can take hours. Trust us. It's worth it.

Downgrade iphone 3g firmware

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