@kanishou good points here, except you might not have taken into consideration that WP7 is a standalone platform with little backward compatibility with Windows Mobiles, and that Microsoft has already announced the launch Windows 8 on ARM, which can run native (recompile) Windows applications which WP7 platform is also incompatible with.

As Elop was a senior executive of Microsoft, he should have well aware of the new mobile strategy with Windows 8/ARM. Even in the very rare circumstance he didn't know, Elop's decision on buying WP7 is way after the announcement Windows 8/ARM, he shouldn't have ignored it.

It's so obviously that he's well aware of the present situation and future prospect of WP7 and still strike the deal with Microsoft. Everything Elop does would not make any sense if he has no hidden agenda with Microsoft.

You might not believe the board would approve Elop's action. How would it sound like if the board actually support Elop? I cannot go into too much detail on it as it'd be rather off-topic in a tech board.