Samsung said this week it has shipped more than 1 million Galaxy S smartphones in the U.S., roughly six weeks after they were put on sale along side the iPhone 4 at AT&T and to T-Mobile subscribers.

Though they aren't iPhone 4 or iPad uptake numbers, sales of Samsung's Android-based phone does give the Android camp a hot-selling model to go head-to-head against Apple, and Research in Motion, which has seen lackluster sales of its new BlackBerry Torch, the first model sporting the new BlackBerry OS 6. Android's momentum has been well documented, most recently by Gartner when it reported that smartphone makers had shipped 11.2 million Android-based devices in the second quarter, or 17.2 percent of the worldwide market, up from a mere 1.8 percent in the second quarter of 2009. Yet much of Android's success has been attributed to the fact that there are dozens of makers and models of Android phones, offered by all the major wireless carriers, while the iPhone remains exclusively on AT&T in the U.S. and RIM is the sole supplier of the Blackberry.

Though Samsung's Galaxy S is sold by all four national carriers, plus the major regional wireless companies, those initial 1 million units came only from AT&T, whose subscribers can also choose an iPhone, and T-Mobile, the smallest of the four national brands. (AT&T's model is called the Captivate, and T-Mobiles is the Vibrant.) Sprint's version of the Galaxy S, the Epic 4G went on sale today, and Verizon's, the Fascinate, won't be available to pre-order until September 9.

There's been a lot of speculation about how market-share numbers and relative sales might shift once AT&T's iPhone exclusive ends, reportedly next year. Some expect iPhone to gain a boost and Android growth to slow once iPhone is available on other carriers, particularly Verizon, the nation's largest. But at least now there's a fast-selling Android flagship that can be matched against iPhone 4 to get a better sense of how the two key platforms are faring in the marketplace, as well as to judge the success of BlackBerry OS 6 models that will be arriving in the weeks ahead.