• by Mark Walsh  @markfwal, September 5, 2010

Google's mobile operating system continued to gain ground against its rivals last month as a platform for accessing the mobile Web. Android now accounts for 25% of Web browsing on smartphones in North America, up two percentage points from the prior month, according to the latest data from Web measurement firm Quantcast.

Apple's iOS held roughly steady from July with a 56% share, while Android grabbed share from BlackBerry-maker Research in Motion and other smartphone operating systems. RIM generates 10% of Web use, down from 9% in July, and all others make up 10%. More than ever, it's shaping up as a battle between iOS and Android for dominance of the mobile Web.

Quantcast suggested earlier this summer that the launch of the iPhone 4 in late June might help reverse its decline in share of mobile use, which has slipped from almost 70% a year ago, mainly as a result of Android's proliferation.

But after an initial burst of activity, there was no change in the overall trend, which Quantcast attributed to a high proportion of iPhone 4 sales from people replacing earlier versions of the device rather than uptake from new customers. (Keep in mind that the firm doesn't include iPad and mobile app usage in estimates.)

At the same time, the launch of the HTC Incredible, Sprint's Evo 4G (also from HTC), and the Motorola Droid X this summer helped accelerate Android's gains against Apple's iOS supremacy. For the year-to-date, Android has picked up 18.6% share, while iOS has dropped 11.4%, and RIM has dipped 1.6%.

Supporting the Quantcast findings, mobile ad network Millennial Media last month said Android in July had become the second-largest smartphone operating system on its platform since it began breaking out OS share a year ago. Android accounted for 19% of U.S. impressions, trailing only iOS' 55% share. RIM was third with 16%.

Millennial also reported that Android was the second most popular platform among developers who create apps for multiple smartphone systems. Three-quarters create apps for Android, compared to 100% for iOS.