The number of Korean smartphone users is approaching the 10 million threshold, company data showed Monday.

SK Telecom, the country’s top mobile operator, said on Monday it has registered more than 5 million smartphone subscribers. KT Corp. secured 3.7 million users and LG Uplus Corp. followed with 1 million.

The combined number topped 9.7 million, up more than 35 percent from about 7.2 million at the end of last year.

The three carriers have seen rapid growth in the number of customers swapping their old feature phones for smarter, more user-friendly gadgets over the past year.

SK said its 5 million figure is nearly seven times greater than a year earlier and 20 times that of June 2009.

KT also saw its number of smartphone customers surge 35 percent since late December. LG users nearly doubled over the same period.

Korea’s smartphone boom was accelerated since the launch of heavy hitters such as iPhone and the Galaxy S.

The hottest seller is Apple Inc.’s iPhone, of which KT has sold more than 3.7 million units since Nov. 2009, making up about 23 percent of the firm’s total subscribers.

SK has provided 2.6 million customers with Samsung Electronics’ flagship Galaxy S since June, it said.

The firm said its unlimited data plans, rich product lineup and various application platforms spurred smartphone sales.

“The adoption of unlimited data services fired up widespread use of mobile Internet and brought about the popularization of smartphones,” said Seo Jin-woo, head of the firm’s platform business unit.

In July, SK started offering an unlimited data plan, which led it to see about an eightfold increase in data traffic between then and December. KT launched its own scheme in September.

The telecom operators are working to launch a faster, more reliable network called Long-Term Evolution this year to cope with explosive data growth.

SK said it aims to double the number of its smartphone users to 10 million this year, while KT targets 6.5 million and LG hopes to triple to 3 million.

Market researchers anticipate that the number of Korean smartphone users may reach 20 million this year, accounting for more than 20 percent of the local mobile phone market.

By Shin Hyon-hee (heeshin@heraldcorp.com)