i have an itouch and sadly, most apps do have better graphics then the wii. But the amount of data each app can have is very limited and so the games wouldn't be very long.
Also most people has an 8 gig iphone/ itouch so there wouldn't be enough data for a decent lengthened, good graphics game. The size of the games wouldn't be created that takes up alot of space, counting most people wil also add music and videos.
Even if iPhone has better graphics, the Wii still pwns it, iphone has limited ways of play and limited story line and play time.
Edit: Also itouch doesn't have the camera or text capabilities. For what i know, it can't call people either.
an Iphone can do all those things...BUT....Think about the cost....and the way you would pay like 50$+ month,y for it
Just bring around your Psp and phone/ Dsi+ phone, thats just a cheaper iphone