Nokia has replaced embattled CEO Olli-Pekka Kallasvuo with former Microsoft exec Stephen Elsop. Elsop was previously president of Microsoft’s business division, responsible for the recent launch of the company’s Office 2010 product suite. He will take over as Nokia CEO on Sept. 20.

A change in leadership at the struggling mobile phone giant had been expected for some time. Kallasvuo—a 30-year Nokia vet—took over as CEO in 2006 and was charged with leading Nokia’s transition from a purely hardware manufacturer to a provider of mobile and Web services, including music. Those efforts, however have been somewhat lacking.

Nokia has lost market share in the high-end smartphone market to Apple’s iPhone and Google’s Android platforms. It’s Web services efforts like Comes With Music and Ovi mobile entertainment and music portal haven’t made a real impact on the market. And Nokia has yet to have a meaningful presence in the U.S. market despite its efforts to do so.

That said, Nokia says Elsop is not being asked to change up the strategy at all, but rather is being tapped to better execute Nokia’s current plans.

“The core strategy is solid and Nokia will continue to power through what is a substantial transformation (from a hardware company to a software company),” Nokia wrote in a blog post about the move. “Elop will help to accelerate that (he’s a get-things-done guy) and his fresh eyes and ears will enable him to take a fresh look at big questions as to that strategy is executed.”