This is an interesting thread, especially when I consider who my current employer is. I will say this statistically the number of users of phone books are way down and have been in a steady decline for years. This is especially true in the more metropolitan areas. I have worked for this company for 13 yrs and honestly can not remember the last time I picked up a phone book. I use my phone or laptop, even when out of town.
With the internet and smartphones technology, IMHO it makes no sense to pay for paper advertising and you would be better served with web or electronic directory types of ads. Even the big phone companies are realizing this and putting their efforts into internet directories/advertising. A good
SEO plan, word of mouth, circle of influence, social marketing are where your ad dollars are best spent.
Just my .02 cents which with all thing considered is not much.