Also - I don't know if this point has any bearing on the question, but you generally have to pay for a yellow pages' listing. So you'd be piggybacking on someone else's marketing efforts.
Not just marketing- a LOT of effort goes into getting/verifying/updating yellow pages data, which is why good (and frequently updated) data is so expensive.
Every site I have seen clearly states that you may not reproduce the data. And there are basically only 3 ways to get the data: 1) Buy it from a legit source. 2) Scrape it illegally from other sites. 3) Use your own resources to go door to door collecting the information (or have all the businesses give their information to you).