Users can click on a phone number to connect directly to a business from the mobile with the new Ad tool click to call. Number of Google advertisers using phone extensions on mobile has grown by an average of 28 percent month-over-month globally. Advertisers have seen an 800 percent in return on investment. The mobile-only campaign helped increase calls to restaurants by 40 percent and click-through rates by 539 percent compared to desktop. The cost per click was also two-thirds less than desktop ads.