Well I don't think it takes a scientist to know that all religions are nonsense. Even a child can tell you that.
As for repeating the same thing over and over, think of these religious callers as confused students, and we are parents just listening in. It is interesting watching their little religious minds learn. ie Building the pyramids doesn't mean god exists, that type of thing.
Ideally I truly want one religious believer to agree that their arguments for religion and god are not valid, and for them to question their own beliefs (possible for the first time).
If it helps one child out there (at least) then its all worth it.
Strangely I do find it interesting to hear these believers and their unfounded nonsense. I keep thinking to myself that the compares are going to say, 'You believe in what? Grow up man, that's just nonsense' But I suppose they need to be civil.