This is why, as someone who works at a movie theater, I love the GEICO camel ad telling people to turn off their cell phones. People will laugh, sure, but I will notice a few actually turning off their phones at that point. Then again, most people who patronize the theater I work at aren't so boorish as to be on their phones during the movie - and, I would imagine, most people aren't that rude.
If people are doing stuff that's disruptive, speak to one of the ushers. They generally have the authority and blessing of the managers to boot people who are being obnoxious.