The one and only HSPA provider here in Canada is offering an expensive data access package that includes the Novatel Ovation MC950D USB Modem. It doesn't seem to require the same massive amounts of power, and this thread and this thread suggest that it might be possible to get drivers for it and get it up and running... Any comments?

EDIT: from the website:
EDIT2: Looks like it needs lots of power; comes with a Y-cable, so external battery pack needed.

All I can say is that the N900 is looking more and more amazing all of the time; these things seem to need lots of power, but the new tablet will need a long battery life...