Google mobile ads with the 'click to call' feature have a 6-8% higher click through rate than those that don't

"Surojit Chatterjee, senior product manager of mobile ads for Google, said campaigns with the click-to-call feature report 6-8 percent higher click-through rates than ads that don’t have it. He said for a feature that rolled out less than a year ago, click-to-call is having a meaningful impact with both advertisers and users. He said it also proves how much more focused mobile users are on fulfilling immediate actions. “On mobile phones, people are looking for things they can act on immediately,” Chatterjee said. “It shows that mobile users, if they find the right ad, they will act on it.”"
Source:  GigaOM, 21st December 2010