Utilizing latest iTunes 9.2 and Apple iOS 4.0 .ipsw firmware file, users can manually update iPhone & iPod Touch to iOS 4.0 latest firmware by themself on either Windows or Mac OSX. Generally Apple iOS 4.0 final build has been released and users can update directly via iTunes 9.2. Instead of using over the air update, you can manually upgrade your iPhone OS firmaware to iOS 4.0 latest build following this guide.
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7 Steps Manual iOS 4.0 Upgrade for iPhone and iPod Touch on Windows and Mac OS
1. Download iTunes 9.2 setup file and install it
2. Download Apple iOS 4.0 firmware .ipsw file according on your iDevice (iPhone 3Gs, 3G, or iPod Touch)
3. Connect your iPhone or iPod Touch to PC / Mac
4. Run iTunes 9.2 and click on your iPhone/iPod Touch from devices list
5. Hold [Shift] key and click on [Update] button.
6. Then browse & select the iOS 4.0 firmware and click on Open.
7. Wait while iTunes updates iOS 4 on your iDevice.
Finally your iPhone or iPod Touch is now running iOS 4.0, the famous Apple mobile OS without having to jailbreak. However you may consider to jailbreak and unlock your iOS 4 iPhone 3Gs/3G to be able riding on any mobile carriers / mobile operators.
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