Microsoft announced they will be launching mobile banner ads to advertisers interested in reaching customers using mobile Hotmail and Messenger. This is a natural progression for Microsoft to continue its pursuit to compete with Google in two playing fields: Mobile and Advertising. While Google's mobile advertising model is based on a more open-ended network (Adsense publishers can be anyone), Microsoft's staple of users on Messenger and Hotmail is pretty sizable in itself. In addition, its mobile operating system has had a first mover advantage with a large user base.
My only concern is if Microsoft can deliver a solid mobile ad platform with reliability and usability for its advertisers. As a paid search marketer, we find the user interface with Microsoft's search engine advertising to be a bit cumbersome. When compared to Google's adwords platform, it just doesn't feel as intuitive and easy to use. If Microsoft is to be taken seriously in its mobile advertising effort, they should focus on this area.
Microsoft will now join Google, Yahoo, Third Screen Media and AdMob to the mobile advertising space.