There are plenty of ways to measure smartphone marketshare. IDC measures units shipped from manufacturers whereas Gartner measures units sold to consumers. Then there's comScore, the research firm that conducts monthly surveys in the US to measure the total number of devices (and thus operating systems) currently in use. Its latest data is summarized above for the three-month period ending in October. See those yellow lines? If our kindergarten skills haven't failed us, then this data shows iPhone usage surpassing the once mighty Windows Mobile OS for the very first time. Unfortunately for Microsoft, Google's Android OS is set to accelerate significantly by the time the February 2010 data rolls in as is WebOS just as soon as Palm can bring its fledgling OS to Verizon's subscriber base. What's most troubling to Redmond about this report though, is where we found it: on FierceDeveloper, a site for mobile software developers who will presumably use the data to help determine which platforms deserve their focus. Oh Windows Mobile 7, where are you?