Steve,
Good luck with the experiment! However, my experience with yellow pages had told me that you won't get much new business from a listing. It will certainly help when someone is looking for your number. Being that it's free, it can't hurt, but if it doesn't work, i wouldn't say that mean yellow pages don't work.
I used to be in the yellow pages business. The reality is the top 3-5 ads get 75% of the calls. people will browse through those ads looking for reasons to call that one. Typically people may call 3 places to get more info. Usually the only time they'll start dialing listing is when they need an answer right away and can't get a hold of the ads they've called. So the good part of that is when someone calls you from your listing, they are probably ready to book.
If i can't be in the top 3 ads in a book for a reasonable rate, i won't go in the book.
Every book i've been in has been worth it. Most cities have more than one phonebook. I don't go in the phone company book. In cleveland i go in the yellow book. Rates are less than half and results are just slightly less than the At&t book.
So check out other books in your area. Most will bargain with you to get your business. If they can't, they can throw in extra ads. I got them to throw in extra ads under weddings and karaoke to go along with my ad under disc jockey in most books.
The most import thing is to check the results. The best way is to have a special number that is only in that book(like you have now). i have different numbers in different books that all get forwarded to my phone.