Google appears to be gearing up to launching a 'Pay-Per-Call' in the same way they handle pay-per-clicks.
"Google sent out notification to its AdWords advertisers that this month “your location-specific business phone number will display alongside your destination url in ads that appear on high-end mobile devices. Users will be able to click-to-call your business just as easily as they click to visit your website. You’ll be charged for clicks to call, same as you are for clicks to visit your website.”
On most smartphones, phone numbers typically can be touched (or “clicked”) to initiate a telephone call. This “click to call” scenario already exists for Google organic local listings on smartphones. What Google is saying, simply, is that it will allow phone numbers to display in ads and will charge advertisers when calls are initiated accordingly.
This is a version, effectively, of “pay-per-phone call” but the cost per call is the same as a click — a bargain (generally speaking) for the advertisers to receive a “warm lead.”"