it depends on the hotel. Some will just ask you to hold and transfer you to the 800 number. Some do not have access to some of the rates being offered online. Some have local specials or conventions they can book you into.

It doesn't hurt to try, my experience has been it doesn't work all that much, but my favorite one was the Hilton Mystic once, when the website was down, and the desk asked when I called "Are you with the clown convention, if you say yes you get half off the room rate"

Why, as a matter of fact, I am

Oh, and if you ever want a freaky experience, go to breakfast at a hotel when they have a clown conference staying there.