One thing i came to realize with yp and other directories, most cover a wide area, so i was getting calls for jobs 30 -40 miles away, after ten years i've realized that most of my work can be had locally in around a 3-4 mile radius, and i don't live in a city either :
Why advertize to people futher away when more are likely to know you locally and you don't have the fuel costs or time waste either, plus you can direct mail your potential customers easier and more quickly and actually hand pick the sort of tcustomers you want
It's simple but it's worked wonders for my business
What you need to remember is that people or businesses dont use yp if they know a local firm, i've ended up scoring big contracts with local housing groups simply because i live near them and they know me, thats worth a lot more than 2.5 grand for an ad in a impersonal directory
Just my humble opinion
regards
steve