Let me preface this by saying that I'm not 100% sure if there are already Pokemon-like games available on iOS or Android devices. I'd love to be told differently, but for now I'll tell you about ngmoco's Monster Tracker, the closest thing I've seen to a Pokemon style game on mobile yet.
It's like Pokemon in that you'll be able to find, capture, train, and battle monsters of different elemental abilities against others. You'll have multiple attacks at your disposal in the turn-based battles, and the more you fight the stronger your creatures you'll get. You can also upgrade your monsters by feeding them other monsters you've captured in the game. Yes, actually feed your monsters other monsters.
Unlike Pokemon, the exploration feature is very limited as you're just tapping somewhat randomly on the screen in rather small environments. The locations themselves are pretty, and have a nice touch interface, but don't go thinking you'll be exploring towns and running back and forth through tall grass hunting monsters.
Not my exact dream monster hunting game, but it's a step in the right direction at least. Expect Monster Tracker on iOS and Android later this year for free.