The Nokia management used the Microsoft money to buy Siemens part of NSN (Nokia Siemens Networks) and managed to turn it around somewhat, in a situation where it looked like Ericsson and Huawei were going to be the only survivors.
I was working for a subcontractor to Nokia during 2010-2016 and we were dumbfounded in the beginning, but as the years went on that turned into a belief that Nokia scammed Microsoft in that sale.
That's what I've heard too -- They knew they were going down and simply took the opportunity to dump the handset business on Microsoft while securing funding to allow the network business to grow.
I think that's the more likely explanation. Remember that Steve Ballmer was crazy enough to also try to buy Yahoo, which would have been an even bigger disaster for Microsoft.
Paralel to that N900 was shapping up quite well, also using Qt as part of its SDK.
Being asked to throw away their Symbian Java and Qt for Windows 7 pure .NET SDK was what made the large majority abandon ship.
Naturally Elop was just driving Nokia into the position he could benefit from his compensation clauses given to him by the Nokia board.