From what I hear, that usually ends badly for the Christian, as the JW's tend to be well-versed in their favorite scriptures and the apologetic for their point of view. Glad to hear it (sort of) works sometimes, though. 
Not if you know the Book backwards, forwards, and inside out like Grandmother did. Until buzz_knox mentioned his buddy doing it I thought she was the only person who could make JWs get up and leave. Well, without threatening them.
.............
A portable phone I had for several years was fun to play with because the greeting was recorded with the handset. I put snippets of movie dialogue on it, once used the "loud stereo in the background to fool people into thinking I was really on the phone" gag, even had a friend who's fluent in German help me with putting a boilerplate greeting in German on the machine once. It kept the nuisance calls to a minimum in the days before the Do Not Call list.
My favorite, though, was when I was Web-surfing and happened on a .wav file of an M-60 MMG firing a burst. I downloaded it and made a new greeting right away. I recorded a couple of bursts followed by me screaming, "FOR THE LAST TIME! NO, I DON'T WANT A COPY OF THE WATCHTOWER! GO AWAY!", followed by another burst. My sister's husband called and heard it and laughed so hard he couldn't leave a message. I got a lot of positive feedback on that one.
