The Economist on Pay-per-call
The Economist talks about the future of online advertising, and squarely validates the potential of pay-per-call by calling it "the next step" after the pay-per-click model which is working so well.
It then talks about pay-per-sale being the "holy grail" of advertising, because this would be the ultimate performance-based marketing. No advertising wasted at all. Yet the example they cite, Bill Gross' snap, appears to be having a hard time taking off. Too far ahead of its time perhaps?
Link: Online advertising | Pay per sale | Economist.com (warning: must be subscriber to access this article)
UPDATE: Pamela Parker has a great article on Pay-per-call. Check it out