Fans of Disney Channel property "Phineas and Ferb" learned earlier this month they would get a theatrical movie on July 26, 2013. Now they might be heartened to learn that movie is becoming as big a deal as that summer date suggests. Disney is hiring Michael Arndt to write a draft of the script, said a person familiar with the movie who was not authorized to talk about it publicly. Arndt brings some heat--he's of course the writer of "Toy Story 3," for which he was nominated for an Oscar, and also won an Academy Award for writing "Little Miss Sunshine" back in 2007. The initial "Phineas and Ferb" script has been written by show creators Swampy Marsh and Dan Povenmire, who have spent recent months working on that script and continue to work on the show. Unlike "Toy Story"--and the cable series itself--the "Phineas and Ferb" movie will be a mix of live action and animation. A Disney spokesman could not immediately be reached for comment. Although the plotline for the "Phineas and Ferb" movie is still being developed, the film is becoming a priority at Disney. The project will now be produced by Mandeville Films, the company behind another upcoming Disney tent pole, "The Muppets." The TV series, now in its third season and with more than 130 episodes under its belt, tells the story of stepbrothers Phineas Flynn and Ferb Fletcher, who spend their summer holiday working on fanciful inventions, as well as their sister Candace, who's always intent on getting them in trouble with their mother. Meanwhile, the family platypus, Perry, leads a double life as a secret agent fighting the evil Dr. Doofenshmirtz. Disney has been working to turn the property into its next big marketing vehicle: In June 2010 it revved up plans to retail as many as 200 Phineas and Ferb-related items — including boxer shorts and skateboards. The show continues to prove its popularity with solid weekly ratings, while a "Phineas and Ferb" television movie drew nearly 8 million viewers this summer.