A year after moving to Los Angeles, Billy guest starred on the MTV show Undressed. In 2001, Billy made appearances on the Fox drama Boston Public in two episodes. He then made his first of four appearances alongside Mary-Kate and Ashley Olsen in the film Holiday in the Sun, which also starred Megan Fox and Billy’s good friend Ben Easter. In 2002, Billy got his big break playing Kyle in the ABC sitcom 8 Simple Rules alongside John Ritter, Katey Sagal, and Kaley Cuoco. Billy has more recently appeared in Headless Horseman, The Strip and Detention.