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Hi There! Chances are, this is going to be an uphill battle; the ability to compete successfully with the likes of Google's own location-based packs of results + organic results featuring individual business websites + powerhouse directories like Yelp is going to depend on the resources you have to put into the development and marketing of the directory. The competition is stiff for anyone entering the directory scene these days, but if you're creating something that doesn't yet exist, the best hope would be in becoming THE authoritative source for the niche. What can you do that will add value users can't get from Google 7-packs or Yelp's reviewers? What kind of content can you create that will earn you a spot amongst these already-established players? These would be the questions I would be asking myself to determine whether I wanted to dive into this new venture.

I agree with Ryan, This is essentially a link wheel, and seems like it will have short terms success. Always link with a purpose and have the user experience in mind.

I agree with Miriam and give a thumbs up to her thorough response. I would only add that not having an additional number for the separate business is pretty inexcusable.  With Skype, Anveo, or any other myriad of VOIP and cell options, getting another number is a dirt cheap cost for someone running a legitimate business. Plus the value it adds for the business should more than cover the $50 or so they'd spend yearly.  If they still want the number to ring to the same line, the could just set up call forwarding on the new number... Again, all that should cost less than $100 a year and probably be even cheaper than that.  Best of luck!