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. On the iPhone 3G and the second-generation iPod Touch, those devices running this OS still has the "iPhone OS 4" branding.

Home screen

 * Folders have been added for app organization.
 * The home screen wallpaper can now be changed.
 * The home screen now allows showing up to 135 pages of apps (2,160 apps in total).

Multitasking
Multitasking support via the App Switcher has been added. It can be accessed by double-clicking the home button.

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.
 * Digital zoom up to 5x 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.

Mail

 * The Mail app now features a unified inbox, which can be used to display emails from all added accounts.
 * Support for MobileMe e-mail aliases and multiple Exchange accounts has been added.

Safari

 * The default search engine can now be set to Bing.
 * iOS 4.2.1 adds the "Find on page" feature.

App Store
Users can now gift apps to other Apple IDs in the App Store

Keyboard

 * The spell check feature has been added.
 * iOS now supports the use of Bluetooth keyboards.