They write:
We randomly sampled 5,000 numbers from our crowdsourced MetaPhone dataset and queried the Yelp, Google Places, and Facebook directories. With little marginal effort and just those three sources—all free and public—we matched 1,356 (27.1%) of the numbers. Specifically, there were 378 hits (7.6%) on Yelp, 684 (13.7%) on Google Places, and 618 (12.3%) on Facebook.
What about if an organization were willing to put in some manpower? To conservatively approximate human analysis, we randomly sampled 100 numbers from our dataset, then ran Google searches on each. In under an hour, we were able to associate an individual or a business with 60 of the 100 numbers. When we added in our three initial sources, we were up to 73.
How about if money were no object? We don’t have the budget or credentials to access a premium data aggregator, so we ran our 100 numbers with Intelius, a cheap consumer-oriented service. 74 matched.1 Between Intelius, Google search, and our three initial sources, we associated a name with 91 of the 100 numbers.