Yellow pages ads are a double-edged sword.
If your ad is dominant or among the dominant then yes you WILL get calls, but if your pages cover a large geographic area then you'll get calls from all over hell and creation.
I know I did.
I just spent ~$1200 bucks on some direct mail and bagged $11,200 in new annual accounts (the calls continue to come in).
All in my PREFERRED area of operation and in my existing neighborhoods.
This has been the best advertising money spent so far.