• In February 2010, smartphones accounted for 48% of AdMob’s worldwide traffic, up from 35% in February 2009. The strong growth of iPhone and Android traffic, fueled by heavy application usage, was primarily responsible for the increase. In absolute terms, smartphone traffic increased 193% over the last year.
• Feature phones declined from 58% to 35% of AdMob’s total traffic as users began switching to smartphones. Although the share of traffic from feature phones as a category declined, in absolute terms traffic grew 31% year-over-year.
• The mobile Internet devices category experienced the strongest growth of the three, increasing to account for 17% of traffic in AdMob’s network in February 2010. The iPod touch is responsible for 93% of this traffic; other devices include the Sony PSP and Nintendo DSi. In absolute terms, mobile Internet device category traffic increased 403%.
• In February 2010, the leading smartphone operating systems in the AdMob network were the iPhone OS, Android, and Symbian. Over the last year, the iPhone increased its share of smartphone requests from 33% to 50% while Symbian’s share of requests fell from 43% to 18%.
• Android was the fastest growing operating system in the AdMob network year-over-year. Android’s share of smartphone requests increased from 2% in February 2009 to 24% in February 2010. The top five Android devices worldwide, by traffic, were the Motorola Droid, HTC Dream, HTC Hero, HTC Magic, and the Motorola CLIQ.

From: http://metrics.admob.com/wp-content/uploads/2010/03/AdMob-Mobile-Metrics-Feb-10.pdf