You can't do this on the iPhone: a new app is available on the Android Market that allows users to sync up their Wii controller to play games on any device running Google's mobile OS. Android Wii Controller IME is available as a $3.99 download. After installing, users simply change their input from the standard Android keypad to "Wii controller," and then wirelessly sync the controller in a simple 5-second process.
The primary purpose of the app is to make it easier for users to play old-school games through the myriad of NES, SNES, Genesis, etc. emulators available on Android. However, it also acts as a fully-functioning control device. So any app that allows for standard keyboard input works with the Wii controller configuration. Here's a Youtube video (originally posted on NintendoLife.com) that showcases the functionality of the Wii Controller Android app: