I think the most likely thing for that would be a 3rd party app once the iPhone is finished getting "unlocked". I think that if Apple had intentions to support those files, they would have included more than just a file viewer. If you get one of those files as an attachment, you have a very nice file viewer to read the files, but you cannot edit the files.
Hopefully OpenOffice will be an option on the iPhone in the future though -- that'd be really slick.