Jason Lee was meant to have a larger role in this film, but his screen time was rewritten shorter than planned due to scheduling conflicts with My Name Is Earl (2005). Most of his scenes were filled in with Zachary Levi's character, Toby Seville.
Ross Bagdasarian named the Chipmunks after executives at Liberty Records, who released Seville's and the Chipmunks' original albums. Alvin was named for company president Alvin Bennett, Simon for company vice-president/record producer Si Waronker, and Theodore for recording engineer Ted Keep.
The trivia items below may give away important plot points.
Some of the the things that happen to Simon are hinted at earlier in the film i.e. falling into a bedpan, picking up Toby's half-eaten apple, and complaining that he feels like he's "living in a dumpster." Also, Theodore is standing next to a brochure for the Los Angeles zoo in one scene.
(at around 32 mins) When the chipmunks are playing dodge ball, Alvin tells himself to remember his five D's- dodge, duck, dip, dive, and dodge. Justin Long who plays Alvin also acted in the movie Dodgeball: A True Underdog Story (2004) where the coach also tells him to remember these same five D's.