Freemium model is widely using in Mobile App. You can play the games without any charges, but if you want to get some extra functions, you need to pay. For example, you can pay some money to get some extra weapons for game characters. There are many successful stories.
We(AdvGen) are trying out this model. The users can use our free version with the basic function. If they want to have some more advance functions, they need to buy the premium version. In the way, the users can try the app first, they can see whether the app is suitable for them and the free version can worth the trust from the users at the mean time.