A San Francisco company called Ingenio has developed a Web advertising system that helps smaller businesses make better use of powerful tools like Google’s new local search service and Yahoo’s online yellow pages.

Most companies that advertise on search engines today pay a certain amount per click to their ad. Problem is, too few of those clicks result in an actual qualified lead, let alone a sale. By attaching a unique phone number to each ad, Ingenio is able to charge advertisers only when their ad results in a phone call from a prospect.

More here.