What mobile technologies can teenagers use to increase exercise?

Calorie and exercise: There are some good apps that can both estimate caloric expenditure and some that can guide you through a workout. Lots of great stuff out there. The hard part is still getting yourself to do it!

Gamified app/device?: There is no easy answer to this. Many companies have assumed that there will be a magic bullet mobile app. There is none. There might be a need to target parents more than kids, but still there would be the issue of teen backlash. Go with things that are fun, like school sports, create an app for a youth sports league, reward families for making and eating healthy meals and for exercising, etc.