If you've ever thought about how great it would be to have your Wii with you when you're on the road, you should definitely check out Tennis Slam. Tennis Slam is basically Wii Sports Tennis for the iPhone. Nothing more, nothing less. Except of course that you can't create your own Mii.
You don't actually move around either of your tennis players when you're playing through the game. But you do control serving and volleying the ball back and forth. There are two different control options: accelerometer and touch. The accelerometer method allows you to actually swing the iPhone to make your little players swat away. The touch method is the same, except you don't have to put your iPhone at risk.
It's difficult to get the swing down because you lose track of what's going when you're not looking at the screen. Plus trying to register what's going on when you bring it back to center. The computer player is pretty quick too, so it's much easier to just stick with the touch method than actually swing it.
Tennis Slam does have a certain appeal to it for those of you who enjoy simple games. It does feel exactly like Wii Sports Tennis, but actually looks a lot sharper. When you simplify it though, it's unfortunately just a glamorous game of pong that will get boring after awhile.