Research in Motion, the BlackBerry manufacturer, announced today that it underestimated last year’s fourth-quarter subscription additions by 15 to 20 percent. Last December the company said net subscriber account additions would total 1.82 million, but a more accurate count shows 2.09 million to 2.18 million new subscriptions.

Research in Motion credits the increase to the popularity of smartphones throughout the holiday selling season. BlackBerry is believed to have around 14 million subscribers.

“BlackBerry smartphones proved to be a big hit throughout the holiday selling season and we’re pleased to see RIM’s business momentum continuing in the new year,” said Jim Balsillie, co-chief executive. “The seasonal slowdown in net subscriber account additions that we expected in the new year did not occur and our focused execution with partners has continued to produce strong results within both enterprise and consumer segments.”

Research in Motion will report fourth-quarter figures on April 2. The company expects quarterly earnings per share of 66 cents to 70 cents on revenue of $1.80 billion to $1.87 billion. Analysts surveyed by Thomson Financial expect a profit of 69 cents per share on revenue on $1.85 billion.