We just went back into the yellow pages after a few years off to build our service division up more. We went with a full page. It's been our experience in the past that the smaller ads don't get many calls and the calls they do get are bottom feeders looking for a bargain, not quality. In your area a full page may not be needed if nobody else is doing big ads, but you want to be one of the larger, more colorfull ads. If there are several books in your area, go with the major phone company or most popular book first, the other will be cheaper, but they are cheaper for a reason.
That said, don't buy more than you can afford. Just keep in mind the cheap ad may not pay for itself. Clear as mud.
