According to research firm Gartner, Google's (NASDAQ:GOOG) Android platform captured 50.9 percent of all smartphone sales to end users in the fourth quarter, cementing its market share dominance. Unlike many research firms that track sell-in to the channel, Gartner tracks sales to end users. The firm found that Apple's (NASDAQ:AAPL) iOS accounted for 23.8 percent of smartphone sales in the quarter, up from 15.8 percent a year ago, while Symbian sales plunged to 11.7 percent of sales, down from 32.3 percent in the year-ago quarter. Research In Motion's (NASDAQ:RIMM) Blackberry took in 8.8 percent of sales, down from 14.6 percent in the year-ago period, and Microsoft (NASDAQ:MSFT) managed 1.9 percent of sales. Like other research firms, Gartner noted that in the fourth quarter, due its record 37 million iPhone sales, Apple  became the world's largest smartphone maker and surpassed LG Electronics as the world's third-largest handset maker overall. Release