Google announced yesterday that it would bring its contextual text ads service, AdSense, to the mobile web. AdSense for Mobile will allow mobile web site publishers in 13 countries to monetize their content with text ads using the familiar pay-per-click model.

Analyst Frost & Sullivan predicts that the mobile advertising market will reach $2.12 billion in the US by 2011. Worldwide, the outlook is even rosier: $10 billion per year by 2010 says the Shoesteck Group, while EJL Wireless Research estimates a $9.5 billion yearly global mobile ad market by 2011.

The thirteen countries that will see the initial roll-out of AdSense for Mobile in the next few weeks are the United States, England, France, Italy, Germany, Spain, Ireland, Russia, Netherlands, Australia, India, China, and Japan.

Google’s foray into mobile advertising has predictably fueled further speculation into the possibility of a Google phone, or mobile operating system. “Google is widely believed to be working on some kind of mobile operating system software or perhaps even a mobile phone to ensure its efforts to distribute ads aren’t undermined by the owners of proprietary wireless networks and handsets,” wrote the Associated Press. Google declined to comment.

Google’s AdSense for Mobile comes in two formats: single and double. Google’s AdSense publisher terms don’t appear to have been updated, so theoretically, mobile publishers could place up to 3 ad units on their content (i.e., up to 6 ads). I wonder whether text ads will have the same sort of success on the mobile web that they have had on the general Internet. Clicking on links often requires more work on the mobile web and screen real estate is so limited that ads might be seen as more invasive.

Also making mobile ad news yesterday was Nokia, who acquired Enpocket, a Boston-based mobile ad provider. Red Herring looks at Nokia’s purchase as a reflection of the company’s announcement last month to transform itself into a software and services company.