Too bad, we can't get the exact timeline for those calls, it would be really interesting.
Okay, he could have got the contact infor from MW's cell phone, but to know the work times (I don't know whether MW's mother works in a job with irregular times) can be iffy or easy, depending on the job. To know the job of the mother however, demands either extensive stalking or getting this info out of MW while he had her.
If it was extensive stalking, it would tell us only how thorough he is, how obsessed with what he does. But if he forced the information out of her, it means, he planned it from the start.
The point in this is, why? Why did he call in one case, not in the others? What was different, what changed and changed back? To me it still looks like he thought, someone was on him and he felt the need to put out some red herrings. Which would explain a later attempt to pose as someone else and check in whether the trick worked. But that is of course only theory and my opinion. Well not opinion, rather an open question.
