Millennial Media: #Android rules in July, #WindowsPhone 7 growth is big | ZDNet:

Android retains the number one position among mobile platforms for the eighth consecutive month with 61 percent of all ad impressions served. Apple’s iOS was the next most used mobile platform with 21 percent of impressions. Apple is still the number one mobile manufacturer with 26.45 percent of the market and Samsung number two with 19.11 percent. Note these numbers are based on ad impressions served during the month of July 2011 and not device sales.

Windows Phone 7 generated only 2 percent of ad impressions during the month, but encouragingly had a 71 percent increase month-over-month. The indicates that more of these phones are in the market each month, and with Mango due to launch soon WP7 could be poised for good growth.