The guys at FierceDeveloper have put together this nifty chart showing the top smartphone operating systems by number of active users in the United States in October, based on comScore's data.
What's interesting about comScore's latest number is it's the first time iPhone OS market share has surpassed Windows Mobile. According to the data, approximately 36 million Americans are smartphone owners, with 40% of those owning Blackberries and 25% owning iPhones. Windows Mobile share has shrunk to 20% and with the increasing popularity of the iPhone and Google's Android OS, it's not looking too hot for WinMo.
Below: the chart of comScore's data. The yellow bars are the most recent statistics.