Would be cool if they would or buy out Nokia.
http://www.phonearena.com/news/Microsoft-hints-it-could-make-phones_id45192
http://www.phonearena.com/news/Microsoft-hints-it-could-make-phones_id45192
Microsoft doesn't make hardware and I doubt that's likely to change.
That they might put their logo on the case of a phone would surely sour the interest of competitors in making Windows Phones as those who buy Windows phones already place an undeservedly high value on Microsoft as a technology leader.
Given what Microsoft has done to acquisitions over the years, I'm not sure anyone would like to see Nokia die like that.