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Google's all about the mobile ads nowadays; it acquired mobile ad network AdMob for $750 million last November, and AdWords (those contextual sponsored links in search results and the like) went live on iPhone and Android a year ago.
YouTube has experimented with mobile ads in the past, running exclusive campaigns with select advertisers and deploying ads to some users in the United States and Japan. Sony advertised the DVD release of recent Oscar-nominee District 9 on YouTube mobile, for example.