I simply think this medium of advertising is not effective anymore and darn sure not a good return on your investment. Couple things to think about - myself and most younger folks do not even use the phone book/yellow pages. If we are interested in looking for something 90% of the time we are going to use the internet - in particular google or yahoo - the most popular search engines. So I think for less money you could start a decent web page - pay bill for keeping it up and use money for google/yahoo add words. You can make the choice how and when your advertising dollars are spent and spent during more key times with more properly directed content. All that vs. a page that will sit in the same book that most of the population really does not use anymore.
Add to that the return on your investment of either the above mentioned or door hangers - I am sure since both my suggested methods you will able to tell if your advertising dollars are working for you with ease - and you would find if you spend the same money doing both of my suggestion and the yellow pages you find a much better return on your money with my suggestions.
Damn yellow page people are just to greedy and overpriced, I think we need a illegal version to start low balling and bring the industry standard down..LOL