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Apple's iOS 4 was released today ahead of the launch of the iPhone 4, which becomes available June 24. iPhone users can update to the latest OS via iTunes, but some features will not be available for the iPhone 3G and the update is not available at all for the original iPhone. iOS 4 will not be available on the iPad until this fall. Apple says there are more than 100 new features in iOS 4, but the most notable tweaks include multitasking, with handy controls for switching apps; home screen folders that you can name by category for easy access to similar apps; a unified e-mail in-box so you no longer need to switch among accounts; and many more....