Google (Nasdaq: GOOG) will start showing AdWords ads within Google Mobile Search in the next few days, although it will only show ads for sites whose landing pages can be adapted to fit on a mobile phone screen reports SearchEngineWatch. The ads will be included automatically, with people needing to opt-out if they don’t want their ads to appear on mobile screens. They will be free until November 18th, but from then on customer will get charged for them. Google’s FAQ notes that “Pre-existing mobile text ads running in your account will automatically always win against a desktop text ad during the keyword auction.” It’s unclear how the ads will show up on mobile devices, and how they will be identified as ads—ad displays with more than 70 characters will get shortened so only the headline and URL is displayed on the mobile phone. SearchEngineLand has a copy of the letter that Google sent out.