"Ingenio this week will begin providing pay-per-call ads on America Online's search results pages. Pay-per-call ads, a recent innovation in online ads, look roughly like the pay-per-click ads that the search world has grown accustomed to--but in place of a referring URL, there is a specially assigned "800" telephone number, which connects the prospective customer to the business, and logs the call for billing. "
--Online Media Daily (free registration)
Other players in the field: Thinking Voice and Ziff Leads.
Advertising Model: Pay-Per-Call