Many users have been reporting problems with the iPhone firmware 2.2 upgrade from Apple. It may be that the best way to solve these problems is to take a step back and downgrade to firmware 2.1. Others inadvertently upgraded their phones when syncing to iTunes on their computer and for whatever reason would like to revert.
The process is relatively simple and should bring back the 2.1 version OS to your iPhone. Performing these steps on an iPhone 3G may work, however this article does not cover reversing the 3G baseband update included in firmware 2.2. Remember, taking these steps is at your own risk, and any hacking of the iPhone could render your remaining warranty invalid.
1) Make sure your device is connected to the PC or Mac and choose the iPhone from the menu on the left in iTunes.
2) If the device is not visible in iTunes you must first put the iPhone in DFU mode. Turn the iPhone off. Hold down the sleep and home buttons together for 10 seconds. Release the sleep button but continue to hold the home button until iTunes detects your device.3) Go to the Summary tab. On a PC hold down the shift key and click the restore button. On a Mac hold down the option key and click the restore button.
4) Select the iPhone firmware 2.1 ipsw file.
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5) While restoration is taking place if you receive errors other than 1011, 1013 or 1015 then restart the process with the device in DFU mode.
6) Check the About item in your general settings menu to make sure you have indeed restored firmware 2.1.