Recently, Quantcast debuted mobile web browsing traffic for Quantified publishers. Included in these free reports are statistics which indicate what mobile operating system audiences are using when they visit a site.
There are three categories: Android, iOS and Other. They are depicted in a graph within each website’s audience profile. To access this information, visit quantcast.com and search for a site. In the right column, click Mobile Web. See an example here. Additionally, another graph shows you how much traffic to a site is derived from mobile web browsing versus computer browsers.
Best of all, you can see this information for your own site if you Get Quantified.