Jingle Network has free directory service (uses ad revenue from competitor)
Jingle Network (www.free411.com) has a free directory service. The business model relies on competitor bidding - search for one company and the site serves up a competitor's number - if you select that number then the service bills the competitor.
Oh, and it also raised $26 million in a second round of funding (more). Article indicates that the US market is worth $8b.