Most smartphones now come equipped with accelerometers to check their orientations and their spped in any direction; so there was no inherent reason a phone couldn't be a Wii-like controller.
Enter Aibelieve software, a company out of Taiwan. For a fee of about $40 one can download their software package, called AiWi (www.aiwi-game.com) for any PC, and get the smartphone client from most app stores (it has to be Android or iOS).
The phone becomes a controller for the PC game, much like the Wii or an Xbox Move. It's got a set of virtual buttons on it as well. A number of games for the PC such as Street Fighter IV, Assassin's Creed and Tiger Woods Golf are supported so far.
One interesting thing about the company is that it is working with Commodore, a company famous for low-end personal computers in the 1980s. Commodore went bankrupt in 1994, but the logo is now associated with a motion controller - for which Aibelieve writes the software.