Apple has started allowing developers to submit apps designed to run on iOS 4. The new operating system will be available for current iPhone and iPod touch users to download starting June 21st, and the iPhone 4 will ship with iOS 4 preinstalled starting on June 24th. But developers have been able to pay a fee for a pre-release copy of iOS 4 for a little while, allowing them to build apps for the operating system.
Of course, iOS 4 will support most apps designed for earlier versions of the iPhone operating system. But new apps might take advantage of new features in the operating system, such as multitasking. Most apps available today weren’t designed to run in the background on an iPhone, because Apple expressly prohibited most apps from doing so. That changes with iOS 4 which allows apps to perform certain activities in the background, allowing you to do things like stream music from Pandora while surfing the web in Safari.
New apps may also support the new retina display on the iPhone 4, which has a native resolution of 960 x 640 pixels. Older apps will scale up to fit the new screen resolution, but apps that are designed specifically for the iPhone 4 will undoubtedly look better on the high resolution display.