Strictly by the numbers: iOS/iPhone is one of the least rewarding platforms/devices to target -- when revenue's the goal. These apps don't perform well vis a vis, say, boring old Windows or iOS/Mac or, increasingly, Android apps. If you're thinking about getting into iOS development with an eye towards Angry-Bird style profits, please read this first (and then the other dozen pieces of research on the same topic):

http://communities-dominate.blogs.com/brands/2010/06/full-an...

Relevant quote:

That number times $1.95 per paid app gives the 'most typical app' the total revenues in its lifetime - the full two years of App Store existence - of $1,948 dollars. This is before Apple takes its cut of 30%, so we are left with $1,363 over two years or $682 per year. This is so 'successful' that half of all of the developers of the 164,250 apps - will actually earn LESS THAN THIS. Before you start to cry, remember, there is that Angry Bird game that had 4 million paid downloads and the Bewelled 2 game with 3 million paid downloads. Thats your math there, they are totally skewing the averages, and you are stuck in the 'long tail' indeed. Half of all developers will earn less than $682 per year. Do you still think this is a good business idea?

EDIT: The mathematics are a little depressing, just something to keep in mind. Certainly a successful app is a successful app. Getting there on iOS seems to be a lottery proposition.