Looks like this is getting announced right now, and it may be Symbian (S60) only. More news to follow...

http://www.allaboutsymbian.com/news/...form_allia.php

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Sound like MS Office Mobile will be making its way onto S60 devices next year, starting with the E-Series. There will also be Exchange connectivity involved. Nothing so far about Maemo, but enterprise clients should be pretty happy.