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.
Continuity mistake: Near the end of the movie, Alvin and Dave are discussing something while turning the lights on and off over and over. In one of the shots, Alvin flips the switch down. When we cut back to Alvin the switch is up again, even though he hasn't flipped it back up.
Continuity mistake: During the entire film, the house number on the front of the house that the boys live in changes. In some scenes it's 1516 and in others it's 1958.
Continuity mistake: At the sing-off, when the Chipettes are singing, Ian uses his phone to make a video. At the end, he winks to his phone. However, when the video is seen on a website by some record executives, Ian does not wink.
Continuity mistake: When the bullies are having lunch outside, Simon shows up and says "Quick announcement, I'm in-charge of cleaning." A piece of garbage suddenly appears on the floor, out of nowhere, between shots.
Continuity mistake: While having lunch at school, after Alvin talks about Beyonce, Theo turns around and the angle changes. The bag of chips behind swaps from pointing in an 8 o'clock direction to a 6 o'clock.
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.