Market research firm Nielsen has posted its latest figures on smartphones sales within the U.S. and they show how Apple's new iPhone 4S has helped the company close the gap with devices that use Google's Android software. Specifically, in the last three months, about 45% of U.S. shoppers who bought a smartphone chose an iPhone, up significantly from 25% the previous quarter. Meanwhile, 47% of smartphone buyers went the Android route, down sequentially from a dominating 62%.

Apple's smartphone sales numbers had slipped in previous months as people were holding out for the iPhone 4S launch, which came a year and a half after its predecessor, while Samsung was seeing strong sales with its Galaxy S II handsets. Besides the new iPhone 4S, Apple also Apple also introduced an 8GB iPhone 4 for $100 and cut the 3GS to zero when purchased with a contract, further helping it pick up pace.

RIM's BlackBerry held the third spot during the fourth quarter of the year but the company continues to see a downward trend. According to Nielsen's estimates, its market share tumbled from 7.7% to 4.5% for new smartphone sales between October and December. The decline in sales is even more worrying considering the firm just released new Bold, Curve and Torch models a couple of months ago.

In terms of total market share for Q4 2011 -- as opposed to just recent smartphone acquirers --  Android holds 46.3% of the mobile OS market while iOS grabbed 30%. In third place is RIM's BlackBerry with 14.9%, followed by Windows Mobile at 4.6%, webOS and Symbian with 1.4% each, and Windows Phone 7 at 1.3%.