I'm not sure I see the point of this. Nokia is already signed on to the WP7 platform. Moreover, most of the phones that Nokia makes are not smartphones. Microsoft would be paying a lot of money for a market they're not really interested in.
On the other hand, what if Microsoft bought HTC? They've worked with Windows Mobile phones in the past, they make some of the better non-Apple smartphone hardware, and they'd be a lot cheaper than Nokia. Android would lose a big manufacturer (no more Evo phones), and Microsoft would gain one. I don't know enough about corporate acquisitions to know if this is a practical option though...
On the other hand, what if Microsoft bought HTC? They've worked with Windows Mobile phones in the past, they make some of the better non-Apple smartphone hardware, and they'd be a lot cheaper than Nokia. Android would lose a big manufacturer (no more Evo phones), and Microsoft would gain one. I don't know enough about corporate acquisitions to know if this is a practical option though...