The iPhone was a game-changer for Apple, moving it from a boutique tech company to a boutique tech with mass appeal. The first iPhone hit shelves in 2007 and utilized the iOS mobile operating system, which is still in use today and in its ninth incarnation. The iPhone 6s is the latest, released in 2015. While features have evolved in the history of the iPhone, it is primarily known for its robust computing power, highly acclaimed user security, the voice-activated Siri virtual assistant, and a hugely popular mobile app store. Since first availability, there have been more than 700 million units sold, or more than two phones for each man, woman, and child living in the United States.