IOS 7 will support the iPhone 4, 4S, 5, and the as yet unreleased 5S, and 5C. The iPhone 3GS is no longer supported for iOS updates.
iPad 2, iPad 3, and iPad 4 (otherwise known as the new iPad) and the iPad mini can be updated to iOS 7. The original iPad can not be updated.
Only the latest version of the iPod touch — released last year — can be updated to iOS 7.
Older iOS Apps
For those using devices that are not supported by iOS 7 the App Store now allows for older versions of apps to be downloaded. So, if your favourite Twitter app is updated to support iOS7 , you’ll still be able to download the iOS6 version of the app.