Officially released for iOS!
Tesla Model S for iPhone, iPod touch, and iPad on the iTunes App Store
Tesla Model S Beta - Android Apps on Google Play
Here are some pictures from the iPhone app they are testing. It sounds like they are looking to add Android support too but at this time they are only testing the iPhone app according to one of the Tesla employees at the event.
Best feature is the ability to turn on your AC or heat remotely. Elon Musk did say during the event that the car would work by itself to keep the cabin temperature between freezing and scorching on it's own without using a lot of battery power. I left all the photos except the first two the small thumbnails since they're not as interesting.