IOS 4

iPhone, iPod touch and iPad, being the predecceesor to iOS 5 and the succeesor to iPhone OS 3. It was for the iPhone 3G or later, iPod Touch (2nd Generation) or later, and all iPads (iOS 4.2.1 or later only). The update was free and included a multitude of new features.

Trivia

 * Initial release on iPhone 4 and iPod touch (4th generation).
 * Limited support for iPhone 3G and iPod touch (2nd generation)
 * This was the 2nd release to drop support for some devices.
 * Recent version was un-available for the CDMA version of the iPhone 4.
 * This is the last iOS to feature IPod and Voice Control.
 * This is the last iOS to have the Mona Lisa wallpaper on Settings.
 * This is the first iOS to Introduce home screen wallpaper on Settings and Home Screen.
 * This is the first iOS to to use multitasking.

iPhone

 * iPhone 3G
 * iPhone 3GS
 * iPhone 4

iPod Touch

 * iPod Touch (2nd generation)
 * iPod Touch (3rd generation)
 * iPod Touch (4th generation)

iPad

 * iPad (1st generation)
 * iPad 2