Think about the QT cross-platform framework which Nokia invested a lot into and is now available across Symbian as well. QT is open source, and Nokia kept it that way and encouraged its growth after acquiring Trolltech (the producers of QT).
Also Nokia contributed code to the trunk version of KOffice (on which Freoffice is based), which is the office suite in KDE.
I'm sure there are other examples as well.
I wouldn't say Nokia fully embraces open source though, but they are learning and are working with the open source movement, otherwise Maemo wouldn't be here. In time they might become more open themselves (the lack of NDA for the testing of the PR1.1 firmware shows steps in this direction). It is still a corporation though, and it needs to protect its business interests, so don't expect miracles.