• by Mark Walsh  @markfwal, August 18, 2010

Offering further evidence of Android's ascendance, the Google mobile platform last month surged ahead of Research in Motion's BlackBerry to become the second largest smartphone operating system on Millennial Media's mobile ad network.

Android in July accounted for 19% of impressions, up from 11% in June, while BlackBerry dropped a percentage point to 16%. Apple's iOS also dropped a percentage point from June but remained comfortably ahead of both its rivals with a 55% share of impressions on Millennial's network.

The company says its ads reach about 63 million monthly users, or 81% of the U.S. mobile Web audience. Android ad requests in July grew 47% over the prior month, compared to 24% for iOS, and 18% for BlackBerry. Separately, iPad ad requests continued to grow sharply in tandem with rising sales of the Apple tablet, jumping 327% last month.

Based on handset makers, Apple was again far and away the top manufacturer in generating impressions with 35% market share, trailed by Samsung, at 17%, Rim, 10%, and Motorola, 9.5%. Among individual phone models, the iPhone commanded 24% share, followed by the BlackBerry Curve, 6.7%, and the Motorola Droid, which broke into the top three for the first time with a 5% share.

The Droid was one of six Android phones among the top 20 on the Millennial network. Among all device types, smartphones drove 49% of impressions, followed by feature phones, 32%, and connected devices, which increased to 19% from 16% in June.

Android's expansion was also reflected in mobile apps. Among developers who focused on creating apps for a single platform, 39% targeted Android, up from 31% the prior month. Both Android and BlackBerry, which increased share to 11% from 8%, appeared to gain ground at the expense of Apple, whose share slipped from 57% to 49% in July.

Among developers creating apps for multiple smartphone platforms, all were creating titles for the iOS, 75% for Android and nearly half (46%) for BlackBerry.

Looking at app categories, shopping and retail apps broke into the top 10 in July, presumably reflecting an uptick driven by back-to-school shopping. Music apps moved up a few notches from June to the No. 3 slot, representing 9% of app revenue on the network. Games and social networking apps again topped the ranking, with games alone accounting for 47% of app revenue.