Other mistake: At the beginning of the episode when they are driving in the car, the door is opened to make room for the camera outside but the opening is visible in shot. (01:49:00)
Visible crew/equipment: Towards the end, right after they watch the house blow up, you can see a hand holding a black object popping up from the right side of the screen. This happens right before Malcolm says, "Pretty sure".
Answer: Francis is only allowed to talk on the phone at school for three minutes a day. I think the code gives him free access to talk to his girlfriend.