iOS 4 Officially Released: Apple iOS 4 Software Upgrade - 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.

The biggest and most obvious update to iOS 4 is the ability for third-party applications to "multitask"—that is, you don't have to terminate them in order to do something else in another app. This is functionality that has been requested of Apple since the launch of the original iPhone in 2007, and it has been a long time coming. (Only the iPhone 4, iPhone 3GS, and third-gen iPod touch get multitasking.)


-Make sure you are using the latest version of iTunes. Connect your iPhone to your computer.

-When iTunes opens, select your iPhone under Devices in the Source List on the left.

-In the iPhone Summary pane, click Check for Update.

-Click Download and Install. Do not disconnect your iPhone until the update has finished.