The plan was to obliterate Symbian and replace it with Windows Phone. Symbian probably died faster than they planned.

May be the plan was just "get a competitor out of the way." Whether they end up buying them or putting them out of business and purchasing all their patents doesn't matter. Though, hopefully for Microsoft, someone else doesn't beat them out on the latter.

Simply obliterating them kills Windows Phone for good, I cannot imagine M$ wanting such things.

i thought it was to buy nokias patents at a knock down price later.