I have an 8800 with AT&T.
Like the previous poster stated, to use the pre-installed TeleNav software is $10 or so a month.
I installed BBery Maps and Google Maps (best) and both interface fine with the GPS. TeleNav does offer more GPS type functions, like Garmin.
However, for the little I use the GPS, Google Maps and BlackBerry Maps works awesome.
If you're looking for a true GPS solution, get a true GPS. If you're looking for something to help you get somewhere when your lost or look up local business, then I've found my 8800 to be awesome!