AdMob released a new metrics report, focused on the usage of mobile web and devices used for accessing the mobile web:
April 2009 Mobile Metrics Report - Mobile Web vs. HTML
HTML usage means mobile devices visiting normal desktop websites, while Mobile Web means visiting mobile optimized websites (e.g. http://m.mobiledrupal.com).
The conclusions are interesting enough to put them on my blog and not bore you with nonr-relevant statistics :)