Actually, that's incorrect.
You can use the GPS without a data plan and even use it.
http://forums.crackberry.com/f41/gps...t-data-147262/
The main problem is that you have to use a program like Googleak.
In essence what you are doing is downloading every section of an area of a map (from zoomed out all the way to zoom in all the way and every one in between) to your computer, setting up a structured tree folder perfectly, so that when you use a program like Trekbuddy, it pulls maps from your memory card instead of OTA.
However, as I did this on my old Pearl 8110 before I got a data plan on my newer phone, I can say from experience that it takes forever to download data from a region, takes up a lot of memory, and is difficult to get working correctly as everything has to be in a precise order and location.
Cliff-notes: It's possible, but not really viable based on difficulty and time spent to limited gain.