According to comScore the top Smart Phone OS platform in the US is Google Android.
|Top smartphone OS platforms
||Share of smartphone subscribers
|Total smartphone subscribers
|Microsoft Windows Phone
[Tables show three-month average Mar/Apr/May 2011 vs Dec/Jan/Feb 2011. Total US mobile subscribers aged 13+]
Our own Mobile Analytics shows Apple as the dominate mobile platform over the same period. However in June a slight drop can be observed in the US and most other western countries.
These two pieces of data together shows there are a lot of Android users who're going to be accessing the web as much as Apple users very soon. Any web site that's not ready for the impact of Android devices should start to make changes now to ensure a good user experience. By the end of the 2011 Apple will have a far lower share of mobile web traffic.