Grsshppr is right on the money. When is the last time you used a phone book to look up something. There are tons of other marketing you can do, much of it free. Yellow page ads are expensive and you do not get bang for your buck unless you are selling Pizza, the number one item looked up in the phone book. Sorry to suggest this without all the other solutions but there is not enough space or time here to suggest a comprehensive marketing plan. Perhaps offline if you want to talk. Good luck.

P.S. there is a way to test this concept. If you have three lines or a fourth phone line, list that number in the yellow pages and measure how many times it rings over the next year and what your sales conversion rate is. Al.