I'm going to compare the iPhone 4S to a GPS unit. iPhone: -Does more than give you a map & directions. -Access to a 3G network allows the phone to have up-to-date business listings. -Thanks to Siri, you don't have to memorize a set of voice commands. GPS unit: -Dedicated to giving maps & directions. -Works even in areas that lack cell coverage. What feature would the iPhone have to have to convince you to get rid of your GPS unit or not buy a GPS unit?