It's called the CrossConnect App, available on the new-for-2016 Smart ForTwo. The car comes with a docking port that plugs into the radio head unit, which holds your phone in place, horizontally. From there, you run the app like you would any other, and it lets you work through your phone's existing information to use things like a media player, Bluetooth calling, navigation, and more.
The app is free for Android and Apple users. It's a little clunky sometimes, but we like the ability to just use the existing functionality of your phone right there in the car's center console.