As all iPhone users know, each time you make a call or use the maps application, and you exit the application to go see something else, the iOS will display on the top of the screen a colored bar showing that the process on the app you exited is still going; and by just touching that part of the screen it will return back to that app to whatever is doing (calling, following a route, etc) this is a helpful suggestion because while driving you want to have your eyes on the road and not on your phone trying to go back to the navigation app