The only advertising that we do is the yellow pages. When I get a call from a new customer I always ask where they got my number(either word of mouth or yellow pages)so that I can keep tract of my advertising dollars at work.
BUT, you have to be very careful not to go overboard. $125 or so a month doesen't sound like much but when you are advertising in multiple directories it adds up fast. I was surprised to find out that last year I spent over $6000.00 in yellow page advertising.
Needless to say I drastically cut back this year (sales rep not too happy).
One thing that I did find. Both in my yellow page ads and truck lettering a recignisable logo goes a long way. People have called saying they see my trucks all over and recignised the logo. I only have 3 vans and a bucket truck.
Also, I have had a picture of a bucket truck in some of my ads. I've had customers say that this is what caught their eye.
If you have email or especially a web site, mention this in BOLD letters in your ad. You can get a lot more on a web site than a yellow pages ad for a lot less money. A web site doesen't cost a lot to set up or maintain either, if you know the right people (like a high school aged computer wiz)
I designed mine and my secretary implemented it. Besides paying her to do it when she wasn't busy, it costs about $35/ month through yahoo. (www.collelectric.com
In all, I would say that the Yellow Pages is where to spend most (but not all) of your advertising budget, then spend a small amount on a web site but be careful not to get carried away.