Waterloo, Ont.-based Research In Motion Ltd. is throwing Apple Inc. a curveball in the smartphone game: The BlackBerry Curve outsold Apple's iPhone in the United States in the first quarter, according to market researchers at the NPD Group.

For one stretch last year, Apple said it sold more iPhones than RIM, the longtime market leader, sold BlackBerrys.

But in the first three months of this year, the Curve benefited from its widespread availability, since it is sold by all four major U.S. wireless carriers, while the iPhone is available only through AT&T Inc. A buy-one-get-one-free promotion by Verizon Wireless also helped the Curve, NPD analyst Ross Rubin said.

The iPhone slipped to No. 2, while RIM's touch-screen BlackBerry Storm — also available through Verizon Wireless — came in third.

NPD did not release sales numbers along with the rankings, saying those expanded figures are only provided to clients.

Apple doesn't say how many iPhones it has sold, but the company said it shipped wireless carriers a total of 3.8 million iPhones during its fiscal second quarter, which ended March 28. RIM shipped 7.8 million BlackBerrys during its fiscal fourth quarter, which ended Feb. 28.

NPD estimated that RIM snagged almost 50 per cent of the U.S. smartphone market in the first quarter, up 15 per cent from the fourth quarter of 2008. It believes that Apple and Treo maker Palm Inc. both saw their share of the smartphone market drop 10 per cent during that time.

RIM declined to comment. An Apple spokesman did not immediately return a call seeking comment.