Apple has just released the final Golden Master (GM) build of iOS 6 to developers. Although a public version won't be available for existing users until September 19th, developers can use the final version to test against iOS apps in preparation for the new iPhone 5.
Developers will be able to use iOS 6 to add Facebook functionality into existing apps using a newly introduced API. FaceTime and iMessages have also been improved in iOS 6 to unify a cell phone number and Apple ID to allow FaceTime or iMessage communications across Mac, iPad, and iPhone using just a number. Apple is removing Google Maps integration in iOS 6 and the YouTube client, but Google recently released a standalone YouTube app for iOS users to counter the change. Apple's replacement maps app includes a flyover features with 3D models of cities around the world.