Globally, iPhone was the top handset in terms of requests, accounting for 16.9% of the traffic on AdMob's network. It's followed by iPod touch in second spot with 8.4%.
Focusing on smartphones specifically, the iPhone OS accounted for 43% of requests, followed by Symbian with 29%. Android is third with 10%.
However, in the US, Android is in second spot with 17% of ad requests in September - up from 13% in August thanks to growth fuelled by the HTC Dream and HTC Magic handsets.
Five of the top ten handsets in the US have touchscreens, six have Wi-Fi, and six come with embedded app stores, according to AdMob's data. The full report can be downloaded here.