A certain fellow by the name of Edgar Assmann (I am not making this up) used to get a ton of calls from us. I would pretend to be Fabio and attempt to sell him products made by "I can't believe its not butter". Very funny, and he hated me too!
I had good luck with a repeat prank caller recently. He had called a few nights in a row. For the first few nights, I just hung up when he called. Then on about the 4th night, I just acted like it didn't bother me and ended up bs-ing with him for a while about computers or something. He never called back after that.