The plumber just needs to trademark his business and then it's a simple case of trademark infringement, no?
But what this also reminds me of is news organizations' objection to article links on aggregation sites. The difference, of course, is after you follow a link you're "there" (assuming you haven't been framed) and can bookmark it as you wish, and click on all the tasty advertisements.
If "all the plumber needs to do" is to trademark his business name to keep HiveMind from listing him (assuming HiveMind wouldn't just remove him by request), then wouldn't this also work for Rupert Murdoch and his ilk? [conscious use of the negative and inflammatory "ilk," with no small amount of satisfaction]
This fool has wedged himself between the client and business and in the process has hijacked the business' phone number. When helphive goes out of business how many people will still try to contact their local plumber, get a no signal tone and assume the plumber is no longer in business?
http://www.facebook.com/l.php?u=http%253A%252F%252Fwww.datma...
The right approach would be to have the hivemind number say "Connecting you to <phone number>... one moment please", at least being more transparent about the process. I just think there is an ethical way to proxy numbers.
Incidentally, Hotels.com forces you to use their 800 number as well, although they have an established relationship. I often will google the hotel name to get the real number, since you know, I might have questions about the hotel that hotels.com can't actually answer.