When I received a yellow page phone book a few months ago, it was packaged in a plastic sack touting the company's search engine. That makes two points pretty clear.
1.) Yellow page companies are as aware as everyone else that their clunky books are going the way of the dinosaur.
2.) They're not going to let that stop them from trying to con business owners into spending money on their lightly used search engines.
Independent statistical data shows that people generally do not use yellow page sites for searching the internet. They use Google. For those who don´t use Google, they use Yahoo/Bing. The rest of the population is riding the fringes.
Recent Alexa page ranks for various yellow pages, according to Search Engine Optimization for Dummies, 4th Edition:
The real search engine players
How various yellow page search sites rank