Is you follow the Maemo community you see that now the first community SSU (firmware upgrade) for Maemo 4 devices (based on Diablo, N8x0) is available.
I guess it's almost as much open as it can be, right ?
Also, Nokia 770, N8x0 and N900 are all steps that Nokia took in the open source world to learn and see where it can focus its effort in order to differentiate itself among the competition WHILE supporting the open source community.
It's still a huge company that wants to make lots of money, but they SEE the potential in an open device (and N900 shows and the next device based on MeeGo shows it even more).
Of course it's no OpenMoko, but I think with Nokia we're going to find one of the best trade off between open source and closed source. Moreover, Nokia listen. Slowly, but listen.