Research group NPD said that the BlackBerry Curve, made by Research in Motion, moved past Apple’s iPhone in the first quarter, thus becoming the best-selling consumer smartphone in the US.

According to NPD, three of the top five best-selling consumer smartphones in Q1 were products made by RIM. The Storm landed on no.3 and the Pearl at no. 4. T-Mobile’s G1 was ranked no. 5.

The research group said that a ‘buy-one-get-one’ promotion by Verizon Wireless helped push the Curve past the iPhone. However, iPhone may have lost its top position in sales also because it is available only through AT&T.

Now, RIM must secure their position as the smartphone market is expected to get a new version of the iPhone, while Palm’s highly-anticipated Pre is set to launch during the second quarter.

According to NPD, the smartphone market as a whole continues to grow, even as the larger handset market stagnates.