With iOS gaining roughly 30 percent United States marketshare as of Q4 2011 at the expense of RIM, Nokia and Microsoft, new numbers from Nielsen’s latest study show just how much of a duopoly the U.S. market has become. While noting about 50 percent of mobile subscribers in the U.S. are now smartphone owners, Nielsen gave a breakdown of how the two leading platforms continue to dominate as of February 2012:

Even more telling than the total percentage of smartphone owners are the numbers for those who purchased a smartphone over the last three months. For new subscribers, Apple’s iPhone was able to grab 43 percent of respondents. Android’s share stayed the same at 48 percent, showing the new iPhone owners were at the expense of RIM and the “Other category.” Both dropped a combined 10 percent in the U.S. market among those who recently purchased a device.

Nielsen’s numbers in January had the  iPhone at 44.5-percent of recent subscribers, and Android was at 46.9-percent for the month of December 2011. At the time, Apple was up from just 25.1-percent. Meanwhile, Android was down from 61.1-percent in October. When it comes to iPhone’s growth from October, the numbers were largely attributed to the iPhone 4S launch (57 percent of iPhone owners bought the 4S in December). Nielsen’s report from today shows demand for the iPhone among recent smartphone purchasers remained steady through February 2012.

With today’s report, Android and iOS captured 90 percent of recent smartphone subscribers as of last month; the rest of the market is RIM and the “other” category at just 5 percent and 4 percent, respectively.

This article is cross-posted on 9to5Google.com