I have used it on the Palm T|X which runs the same version of the OS as the Centro. The only odd thing about EarthComer is that it needs internet connection for route calculation (which would in theory be better on a smartphone) and there's no automatic recalculation. But otherwise it is very usable. http://www.earthcomber.com/splash/howdoeswork_pda.html
Palm Phones are supported and the app IS free (and so are the maps) so its definetly worth playing around with.
Yeah, the Centro uses tower triangulation out of the box, which isn't that accurate... And Power Hero is a really useful product for management. I definitely recommend checking it out.