I have been thinking about this for some time. Love my Android. Like developing apps. The big question is: How do you make money developing apps on mobiles.
Hard question. IMHO, I don't believe too many folks will make a lot by developing an app that is mainly phone based. Sure a few game makers will, but not too many. Getting eyeballs and the engineering work make that too expensive.
The kinds of apps one needs to figure out are ones where you have some interesting back-end services and the mobile app provides a new means of accessing that. Google/Facebook/Twitter are the great examples, where they have a service that is useful in itself. The mobile apps allows users to access those services at all times and drives more revenue to their services.
Another point. Trying to charge for mobile apps feels like a pretty hard model to scale (of course, that might be my opinion because I am a cheapskate). I don't know how profitable adding ads are either (unless they are very targeted based on your app/user). The model you need to come up with is to either get a reputation for being a good app developer and then doing some consulting based on that. Or creating targeted leads based on your user's needs and getting money from those leads.