Symbian is the big loser; in February 2009 it accounted for 43% of AdMob's smartphone requests, but now it only takes 18%.
More generally, smartphones accounted for 48% of AdMob's worldwide traffic last month, up from 35% in February last year.
AdMob is getting plenty of ad requests from mobile internet devices though, including iPod touch, PSP and DSi. This category now accounts for 17% of the company's traffic.
The full February 2010 AdMob Metrics report can be read here.