According to new market data published today by the NPD Group, The BlackBerry Curve was the top selling smartphone in the U.S. in Q1 2009, regaining the number one spot from Apple’s iPhone.

The NPD report concluded RIM’s total market share for Q1 2009 was up 15% over Q1 2008. The report says RIM now collectively has 50% of the U.S. smartphone market.

According to the NPD report, the top five-bestselling smartphones in the U.S. were:

1. BlackBerry Curve 8300
2. Apple iPhone 3G
3. BlackBerry Storm
4. BlackBerry Pearl (except Pearl flip)
5. Android G1

The success of the BlackBerry can be largely attributed to aggressive marketing campaigns, lower prices as RIM pushes the next generation devices, and mass availability in the U.S. through multiple telecoms.

Apple is continuously improving its iPhone to make the device more appealing to business users. The upcoming iPhone 3.0 OS update is expected to offer integrated push e-mail for Gmail accounts. However, the BlackBerry remains the smartphone of choice for enterprises, while the iPhone is mainly used for personal usage.

The iPhone today also earned another JD Power award for customer satisfaction among consumers. The phones were judged based on the operating system, features, battery function, design, ease of operation. The iPhone earned top rank with 5/5 on all categories except for battery function where it ranked 2/5.

To help maximize market share, there is speculation Apple could be developing two versions of the iPhone, a lower and higher end version to increase sales. There is also speculation Apple is developing another media centric product with Internet calling capability (VoIP) that could be released by the end of the year.

RIM today announced the release of its BlackBerry Enterprise Server 5.0. RIM CEO Jim Balsillie also confirmed today to Reuters the company is working on a new version of the Storm.