Stephen Elop stated that Nokia expects to sell approximately 150 million more Symbian devices before the transition to Windows Phone is complete. Assuming that figure is achievable (which is far from certain) I tried to understand how that figure will affect the volume and share numbers for Nokia in the coming years.
It’s very likely that the first WP phones will not ship in large volumes until 2012. Product development cycles being what they are, unless there is an ODM rebranding (i.e. taking an HTC phone and gluing a Nokia sticker on it) the minimum development time is at least 12 months. Keep in mind that Nokia does not have engineers to build such a product today and hiring them alone can take months.
The following two charts show what a two year forecast that adds up to 150 million Symbian devices looks like. I assumed Windows Phones begin to ship in 2012 and, keeping in mind that WP7 is designed for a higher hardware specification than the current Symbian phones, I show a modest ramp for a total of 15 million units in the first year.