|In-app purchasing is where the money is gonna be, according to developers.|
With Apple's new iOS 5 coming soon, apps on both iOS and Android will have a pretty good set of tools for notifying users... which means more opportunities for in-game purchases. This all goes to show that if you're planning on making money with mobile games, your strategy should not be based on just creating one game and hoping it becomes a mega-hit. Sure, that may happen, but your odds are better buying lottery tickets. A more sure path to revenue is in planning a series of games (connected in some way, or not) that don't cost you a huge amount to develop. Execute them well and build an audience, then try to sell that audience on your other titles. If you have a design that lends itself to in-game purchases, that's even better.
The more games you have out there, the more cross-selling you can do. Also, it improves the odds of one of your games becoming a hit. Of course, this does assume you're making sure each game is a well-polished little gem. Cranking out a series of crappy games isn't going to help you at all. But don't pin your hopes on one title; create a series of games, or a game with lots of additional content and new variations. Make an audience happy with your game, and then you market other things to them. They will also become your best salespeople, especially if you make it easy for them to spread the word about your game.
Once you've got a big enough group of customers that like to give you money, you've got yourself a dependable income. Keep turning out things they like and you won't be worrying about where the next megahit is coming from; you;ll be too busy watching your bank account grow.