I'm running trek-buddy from downloaded maps, and it's pretty decent. Doesn't cost me for data, and can store track maps.
mgmaps also allows you to download maps into a 'cache', as well as download maps you don't have. Not quite awesome GPS, but for a few megs (10 MB is enough to get a decent zoom of the entire JHB/PTA area.) on my phone. I get decent map coverage, using only a 'cheap' bluetooth GPS. Downloading is useful if you happen to want a satellite image instead of the street maps you've got, or if you happen to venture outside your downloaded area...
I picked up the bluetooth GPS for about R300 on a local auction site, which was quite a bargain. Think you can get them for around R600 normally.
EDIT:
The C902 would probably run newer and more advanced software than my old K800i, so you quite likely have access to some smarter apps. Can't recall if you've got S60 on that one.