Google has officially expanded its AdSense for mobile service that converts AdWords ads to text ads, which appear on the Web sites accessed through mobile devices. The Web sites have to be optimized for mobile browsers.
A quote from the article at Search Engine Land:
The idea here is that available monetization will encourage mobile friendly site development. There are a number of other mobile ad networks (with more on the way), including Third Screen Media (owned by AOL), Medio's MobileNow network, Yahoo Mobile Ad Network, Ad Mob, Enpocket (bought by Nokia), among a few others.
The push to target mobile devices comes after Google's decision to also place ads on the popular YouTube video portal. The pay-per-click model (PC World) has been the chief revenue earner for Google. The mobile AdSense network will be open to publishers in 13 countries, including the United States, England, Germany, Spain, China, and India.
More news links:
Google expands mobile Ad Network (Associated Press)
Google AdSense for mobiles puts contextual ads at your fingertips (CNET's News.com)