SK Telecom\'s net profit more than doubled in the fourth quarter, South Korea\'s top mobile operator said on Tuesday, partly as a result of one-off asset sales. Net profit in the October-December period surged to 519.1 billion won ($477 million) compared with 195.5 billion won a year earlier. Operating profit was up 37.6 percent over the same period at 544.6 billion won. The surge in net profit was partly down to revenue of more than 700 billion won from selling property and a stake in steel giant POSCO. The extra revenue was used to help pay for the roll out of next-generation Long-Term Evolution, or LTE, networks which offer quicker connection speeds. A company statement said SK Telecom had acquired 7.53 million LTE subscribers by the end of 2012. South Korean wireless operators have spent heavily to promote the new 4G service -- up to five times faster than 3G -- to accommodate a growing number of smartphone users demanding faster speeds to download videos or play games. One of the world\'s most wired countries, South Korea has more than 30 million smartphone subscribers out of a total population of some 50 million.