Continuity mistake: In the scene where the grandma is talking at the table with Reese and Malcolm, notice the bottle on the table next the the grandma, between takes the cork from the bottle goes from being on top of the bottle to next to the bottle, it changes in almost every different shot.
Continuity mistake: Hal shows Dewey that he fixed the microwave so that it works with the door open. There is a red cloth inside. Hal then shuts off the microwave and when he and Dewey start talking the cloth changes position from shot to shot.
Continuity mistake: When Lois goes outside to meet Hal at the clothesline, she leaves the door open. In a few shots during their conversation, the door is closed in the background. (00:06:20)
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.