When Allie and Samantha are arguing, the power goes off. Then it shows Allie's mom talking on a cord-less phone to a client... one that needs to be plugged in to an ELECTRICAL outlet. Now that's one magical phone.
I agree...that did appear to be a cordless telephone and the power did go out. The cordless phone should not have still been connected. The only way she still would have been connected is if they had a generator, but the lights were out everywhere else in the house...why would they only have a generator powering the outlet the cordless phone is on? It doesn't make sense that way so this definitely has to be a slip-up.