The most fundamental differences between AIR and PhoneGap is that you build AIR applications using tools rooted in the Flash Platform, and you can develop PhoneGap application using HTML, CSS and JavaScript. AIR applications use the AIR runtime, it enables you to have a single code base, with the exact similar expected behavior through all supported platforms. PhoneGap applications execute inside of the native web browser component for each supported platform. For separate platform, PhoneGap may behave differently.