The Scoop on the OS4 update

iPhone and iPod Touch Compatibility With iOS 4.0

• iPhone 3GS: Full iOS 4.0 compatible except iPhone 4 specific features
• iPhone 3G: Partial iOS 4.0 support. Doesn’t support multitasking, wallpaper and Bluetooth keyboard.
• iPhone 2G: No iOS 4.0 support. (Custom Modded 3.1.3 with iOS 4 features available)
• iPod Touch 3G: Full iOS 4.0 support except for iPhone specific features
• iPod Touch 2G: Partial iOS 4.0 support. Doesn’t support multitasking, wallpaper and Bluetooth keyboard.
• iPod Touch 1G: No iOS 4.0 support.

So if you have an iPhone 3GS or an iPod Touch 3G, then you can enjoy most of the features present in iOS 4.0.
Once you have found your iPhone or iPod touch model and decided to upgrade to iOS 4 Firmware, you need to update your iTunes to 9.2 if you haven’t done it already. Only the latest iTunes 9.2 supports iOS 4.0. Also don’t forget to take a backup of your data before upgrading to iOS 4 Firmware.

If you rely on Jailbreak or Unlock, then do not upgrade to iOS 4.0, until you hear from the iPhone Dev team.

http://www.techhail.com/iphone/ios-4-update-for-iphone-3gs-3g-2g-ipod-touch-3g-2g-1g/5123