I use yellow pages and yell.com but dont know if they really work. I think the pages work better then yell.com. They can tell how many calls you have, but a lot of them calls are from sales people wanting you to advertise with them so the figures arent that good. When I do get calls I always ask how they found me and most say they googled w/c in the area. When I tell yell this they say 'How do you think you got to the top of the page, its us thats putting you there.'
I do advertise with google thats free but surely if yell put me at the top of the page then there would be some indication that they had done so, I see no proof i.e links etc.
How I see it is that to advertise is tax deducatable and its good to be in as many places as you can. At the right price of course.