Sony Ericsson's struggling handset company is undergoing an executive shake up in its U.S. branch.

Najmi Jarwala, president of Sony Ericsson USA and head of the company's North American operations, is leaving Sony Ericsson to pursue other career opportunities, the company said in a statement Monday.

Starting April 1, Anders Runevad, executive vice president of Sony Ericsson and head of global sales and marketing, will take on Jarwala's responsibilities until a successor is named.

Under Najimi's leadership we have redefined our North American strategy, built operational excellence, and strengthened our total presence considerably in this very important market, said Dick Komiyama, president of Sony Ericsson, in a statement.

We are sad to see him leave Sony Ericsson after more than three successful years, but at the same time we wish him all the best for his future.

The joint venture between Japan's Sony and Sweden's Ericsson has been beset by problems recently. The company said last week it expects to lose between $460 million and $528 million during the first quarter of the year, as demand for its phones have plunged. These losses are leading to reports that Ericsson may want out of the mobile phone joint venture.

The company has had some success in the U.S. with its Cybershot and Walkman phones but hasn't been able to gain much traction in the high-end smartphone market in the U.S. as consumers prefer Apple's iPhone 3G, Research In Motion's BlackBerrys, and HTC's Touch line of smartphones.

Sony Ericsson plans to focus more on entertainment to help it mount a comeback, as it unveiled a host of services that will bring full-length movies, games, and music to handsets.

In the fourth quarter, Sony Ericsson lost over a percentage point of market share, dropping from 9 percent share in the fourth quarter of 2007 to 7.5 percent market share in the same quarter last year, according to research from Gartner.