The advertiser beside signs a contract that allows them to compete against other advertisers in a private auction hosted by a publisher or, more commonly, an advertising network. Each advertiser informs the host of the maximum amount that he or she is willing to pay for a given ad spot (often based on a keyword), usually using online tools to do so. The auction plays out in an automated fashion every time a visitor triggers the ad spot.
Click-to-call ads are a direct result of the massive adoption of mobile phones in the last decade. Initially phone numbers were added to the websites of local brick-and-mortar stores or found in online and directories. As consumer acceptance of mobile advertising took off, new ad formats evolved to keep pace with the demands of mobile and consumers.
Image Texts or Expanded text ads (ETAs), can run on the Display and Network in a different format than in Search. To boost their impact, display ETAs may, for instance, have a different layout for description lines. They may also appear in native formats and image text formats