- Multitasking :- Now you can run your favorite third-party apps — and switch between them instantly — without slowing down the performance of the foreground app or draining the battery unnecessarily.
- Folders :- Organize apps into folders with drag-and-drop simplicity. Get faster access to your favorites and browse and manage up to 2160 apps.
- Even better Mail :- See messages from all your accounts in a unified inbox, organize messages by threads, open attachments in third-party apps, and more.
- iBooks :- More than a great ebook reader, iBooks is also an amazing place to browse and shop for books, day or night.
- Create playlists :- Create custom playlists right on your iPhone.
- 5x digital zoom :- Get closer to your subjects by zooming in up to 5x.
- Tap to focus video :- While shooting video, tap the display to choose where to focus.
- Faces and Places in Photos :- View photos based on who’s in them and where they were taken.
- Home screen wallpaper :- Change the background wallpaper on your Home screen.
- Gift apps :- Send apps as gifts to your friends or family.
- Spell checking :- A built-in dictionary automatically suggests words and corrects spelling. It works in Mail, Notes, and other apps.
- Wireless keyboard support :- Pair a keyboard based on Bluetooth wireless technology with your iPhone.
iOS 4 works with iPhone 4, iPhone 3GS, and iPhone 3G. Not all features are compatible with all devices. For example, multitasking is available only with iPhone 4 and iPhone 3GS.