I can't answer the question so I haven't commented so far, but I read (into) the original post:
We have a psycho ex-boyfriend calling one of our employees and I want to know if I can block them from being able to call into our system??
I've gotten this question a great many times over the years, and I know where there's a will there's a way with the ANI tables and stuff, but I'll be danged if I'm gonna spend a couple of weeks figuring out how to do it and then the once or twice a year I actually have to I end up not being able to remember how I did it!!