IOS 4

iOS 4 is a version of iOS that was released on 21 June 2010. It is the first iOS version issued under the "iOS" rebranding, dropping the "iPhone OS" naming convention of previous versions, in iPhone 3G and second-generation iPod Touch, those devices running this OS still called "iPhone OS 4".

Home screen

 * Folders have been added for app organization.
 * The home screen wallpaper can now be changed.

Multitasking
Multitasking support has been added.

Camera

 * Tap-to-focus has been added.
 * The LED flash can now be used while taking photos.
 * Support for HDR photo capture has been added.

FaceTime
FaceTime has been added, which allows for video calling.

iBooks
The iBooks app is now supported on iPhone. It was previously only available for the iPad.

Game Center
iOS 4.1 adds Game Center, which allows users to play and challenge friends in games.