Well, here goes, the standard IT answer.
"It depends."
What flavor/OS PDA are you dealing with?
I think the current methodology is web-based, as in MapGuide, for a mobile solution.
Topobase is primarily a specific set of data models and adds some rulle-based object placement with Oracle as a back-end. I'm not sure you would use both GIS Design Server and Topobase together - they are more like different flavors of the same basic technology.