Nokia has joined forces with Microsoft in an attempt to regain ground lost to the iPhone and Android-based devices.
Under the deal, Nokia will sideline its own existing operating systems and use the Windows phone operating system for its smartphones.
Chief executive Stephen Elop said that there would be "substantial" job losses as a result of the tie-up.
Nokia will remain "first and foremost ... a Finnish company. Finland is our home and will remain our home," he said.
But job losses around the world, including in Finland, will be inevitable, he added.
At the launch of the new partnership with Microsoft, Mr Elop said that "the game has changed from a battle of devices to a war of ecosystems".
"An ecosystem with Microsoft and Nokia has unrivalled scale around the globe," he said.
Bing to power search services
Microsoft chief executive Steve Ballmer said Nokia and Microsoft working together "can drive innovation that is at the boundary of hardware, software and services".
Microsoft's Bing will power Nokia's search services, while Nokia Maps will be a core part of Microsoft's mapping services.
The BBC reports that Symbian, which runs on most of Nokia's current devices, will become a "franchise platform", although the company expects to sell about 150 million more Symbian devices in future.
"It is a transition from Symbian to Windows phone as our primary smartphone platform," said Mr Elop.