Media measurement and Web analytics company Quantcast has some interesting numbers on mobile browsing in the United States, and it’s preparing to release some of those statistics, across vendors. Earlier today, the company put up a teaser blog post, showing two graphs, one of them representing the share of mobile Web consumption in the US per mobile OS.

As you can tell, Quantcast concludes Android is storming ahead, now taking up a 25 percent share of total mobile Web consumption in the US. Apple’s iOS, meanwhile, is seeing its share decline, from approximately 67 percent in May 2009 to 56 percent in August 2010.

Provided this trend continues at current rates, Android’s share should be equal to that of iOS in another twelve months, at least according to Quantcast. It’s important to note that both are still growing rapidly in absolute numbers – what we’re seeing is the relative shares shifting.

Research In Motion’s share is roughly 10 percent according to Quantcast, as much as all ‘other’ mobile operating systems combined, but showing no signs of growth whatsoever.

Clearly, the battle for dominance over the mobile Web is being fought by two companies only at this point, and their names are Google and Apple.

In a second graph, Quantcast reports that Android took share from every corner of the market last month. The company adds that it’s the operating system’s best month share gain since November 2009, when it surpassed the 10 percent share mark.

Now, we should point out that another Web measurement company, Net Applications, has just released statistics that suggest iOS dominates the mobile Web far more clearly on a global level.

According to Net Applications, devices that run the iOS operating system (the iPhone, iPod touch and the iPad) accounted for 1.1 percent of all hardware on the Internet last month, compared to a mere 0.2 percent share for Android. This suggests a 6:1 ratio in favor of iOS, looking at worldwide statistics.

It also tells us Android is making strides in the United States much faster than in the rest of the world when it comes to browsing the mobile Web, placing Quantcast’s and Net Applications’ numbers side by side.