Don't limit yourself to just those two mobile platforms - there's a wealth of other platforms with large userbase, and less of a bandwagon of developers in competition (Nokia, etc).

I would also agree with ApochPiQ - don't think you can make millions, because of a few success stories you read And any "gold rush" period when you could make loads of money from something trivial has surely long gone, especially for those two platforms. You could still make money perhaps, but that goes for any platform.

Also check out the (sadly now locked) post about earning $12,000 a year in game development, to put things into perspective. Is this just for extra pocket money on the side, or do you believe you can set up a business to do better than what you currently earn in game development?