I have a Top Spin on my iphone, it costed about 3 euros, so wasn't expensive, but to be honest - the game is just for fun, and i am playing it when i am extremly bored. Also most of the apps are up to 5$, those with higher prices are generally not popular at all. So if creating something for smartphones I would be up to tennis manager, but knowing the iOS and Android reality, the game would be not that complete as on the personal computer.
Also there are plenty of tennis games for mobiles, the one good I played was hmm tennis challenge or something like that, you could even challenge a ball called out

it was very random of course, but the game was really good thus it was pretty hard to move a player, cause the move indicator was much smaller than the top of my finger.