You should understand that commercial in the app or in-app purchases won't really make you a billionaire, because 98% of app revenue worldwide comes from free apps (
source). Your monetization scheme should be unique enough for the users want to pay it seamlessly, and the number of users that can be reached via mobile app will make you the fortune. We've seen so many various monetization models for mobile apps, that if you feel like it should make the money, but if you don't know how exactly -
contact us, and we'll find that unique gold for you.