iOS 4 makes it easy to leave apps without quitting , but what happens when you actually do want to terminate an application? Quitting applications can really help with older apps that have not been updated for iOS 4 “multitasking” and that do not properly return to the state they previously were in when resumed. There’s are two ways you can quit, although neither one is particularly obvious.

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iPhone 101: Quitting apps in iOS 4