Apple has released the third version of iPhone OS 4 and its accompanying Software Development Kit (SDK) for the iPhone and iPod touch. As with prior beta releases, a main Xcode and SDK beta is available for download, as are pre-release builds of the iPhone OS 4 software for the iPhone 3G and 3GS, and the second- and third-generation iPod touch. Changes made in the latest beta have yet to be revealed. Both the new SDK and pre-release builds are available…