Classics such as PacMan and Tetris--which has sold more than one million copies since 2002--are popular, but today's cellphones aren't limited to simple videogames. The most exciting new games capitalize on what differentiates cellphones from other portable gaming gizmos: They let you to talk to or text-message other players midgame; require that you snap photos of real-world objects with your built-in camera; and, in some cases, use GPS to incorporate your actual movements into the game. Of course, there are downsides to gaming on your phone. Keypads are ill-suited to car chases or dragon hunts; unlike console game controllers, most phones can register input from only one key at a time, so you can't simultaneously kick and jump, for instance. Puny screen size can also be a bummer, but new 3-D graphics chips from Santa Clara, Californiaâ€based nVidia will squeeze more detail into those tiny spaces. "We're past the novelty stage," Buchanan says. "We're already starting to get into Game Boy territory."