Apple's share of the U.S. smartphone market has risen dramatically in the wake of Apple's October launch of the iPhone 4S -- and with the mobile OS system gap between Apple's iOS and Google Android narrowing sharply in December, according to a new U.S. mobile user survey released by Nielsen on Wednesday.

Android's mobile OS market share fell from 61.6 percent in October to 46.9 percent in December, Nielsen said. By contrast, Apple's iOS market share climbed from 25.1 percent to 44.5 percent during the same period.

Piper Jaffray analysts Gene Munster and Andrew Murphy now believe that Apple's fourth-quarter iPhone sales were stronger than the investment firm had previously projected.

"Our previous estimate of 30 million could prove to be conservative," Munster and Murphy wrote in a Tuesday investor note. "We are raising our estimate by 600,000 units to 30.6 million."

Commanding a Premium Price

About 46 percent of U.S. mobile consumers overall owned smartphones during the final quarter of 2011, according to Nielsen. Furthermore, 60 percent of the survey respondents who acquired a new mobile device within the last three months said they elected to choose a smartphone over a feature phone.

Among smartphone users overall, Nielsen reports that consumer adoption of Android models continued to lead the field in December with a 46.3 percent share of its survey respondents. Still, the iPhone's 88 percent year-over-year unit shipment growth and average selling price, or ASP, of $640, according to Piper Jaffray, demonstrate that plenty of consumers were willing to pay a hefty premium for Apple's red hot device during last year's fourth quarter.

Much the same trend is playing out in other regional markets around the world, including Europe. "The iPhone 4S is the most expensive," confirmed Francisco Jeronimo, a research manager at IDC.

Samsung's Galaxy Note comes closest to matching the high ASP delivered by Apple's iPhone 4S in Europe, though it is arguable whether "it should be considered a smartphone or a tablet," Jeronimo said in a Wednesday e-mail. Other smartphone models delivering high ASPs in Europe include the HTC XL, Samsung's Galaxy Nexus, the Nokia N9, and RIM's BlackBerry Touch Bold, Jeronimo said.

Gartner reports seeing similar ASP trends in Europe. "I do believe that [the ASP delivered by Apple's iPhone] 4S is the highest," said Gartner Research Vice President Carolina Milanesi. However, Samsung's Galaxy Nexus and the HTC Titan HD come close, she said in an e-mail Wednesday.

BlackBerry Popularity Declines

By contrast, Nielsen said Research In Motion's BlackBerry platform lost a significant amount of traction among smartphone buyers during the closing months of 2011. An unconfirmed media report suggesting that Samsung Electronics was interested in acquiring RIM, either in whole or in part, helped to boost the value of the BlackBerry maker's stock on Wall Street Tuesday.

With respect to U.S. smartphone owners overall, RIM's BlackBerry OS holds a 14.9 percent market share, according to Nielsen's latest survey. Among recent smartphone purchasers based in the United States, however, RIM's mobile OS platform fell to a mere 6 percent share in the final three months of last year.

During the final three months of 2011, Microsoft also struggled to establish a significant U.S. market presence for its new Windows Phone 7.5 platform, which is also known as Mango. Nielsen said growth in Microsoft's share of the U.S. mobile OS market was minuscule: 1.4 percent in December vs. 1.3 percent last October.

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