While it was assumed that Apple will release iOS 7.0 during today's iPhone event, it turns out that the next version of Apple's mobile operating system will be arriving on September 18th. This is just a couple of days before the Apple iPhone 5S and the Apple iPhone 5C are released with iOS 7.0 onboard. The update will released for the iPhone 4, iPhone 4S, iPhone 5, iPad 4, iPad 3, iPad 2, iPad mini and iPod Touch 5 on September 18th.Apple is expecting iOS 7.0 to be downloaded by "hundreds of millions of people". In terms of compatibility, keep in mind that not all the new features will be available across the iOS devices. You can learn which devices will get which features by checking here.
Apple says that iOS 7.0 contains "over 200 features" including the completely revamped UI, the new share menu, AirDrop, new camera features, new "textured ringtones", better multitasking, better battery management, and Siri improvements.
source - Apple