Thanks for the link. If things persist we'll have to do something more "official". After doing some more searching on my own, it seems apparently there is no tech-based solution to this.
The number just appears as "private." She didn't answer, but the guy left a pretty insulting voice mail. It didn't sound like some kid doing a prank call either. It could just be someone with a wrong number, but I wanted to know just for peace of mind.