Continuity mistake: When Ian films the Chipettes during the sing-off, he says, "If you like what you see then call Ian Hawke." But when someone else plays the video back later, he says, "If you're interested, then call Ian Hawke."
Continuity mistake: When Toby comes to get the chipmunks at school he breaks a drum-head. He breaks the same drum-head twice.
Continuity mistake: At the Chipmunk's house, the poster on the wall outside the kitchen keeps changing.
Alvin: Don't worry about picking us up after school, Toby. We'll catch a ride - IN A HEARSE!
Answer: Alvin could have easily known Toby's number and told it to her. Ian just simply put down his phone not even thinking that the chipettes could get at it from inside of the carrier.