The gps puck itself does not require anything but a full charge.
BUT it does nothing on its own really either. You need to connect it to a device with software that can "read" its output - your location vis a vis satellite readings.
Then the device, in this case BB, coupled with software can show certain information such as you current latitude/longitude and maybe elevation. Next, depending on the software, it can show maps and locations and then maybe information about the surrounding restaurants, shops, movies, etc.
There are a few programs that run on the BB that do _NOT_ need data. You can see lat/long. You can even see maps and your location on them if you pre-plan and download the maps to your computer and then copy them to an SD card (need card since they are too large for internal memory on a BB). Trekbuddy and another program.
But most of the software requires data as they pull down new maps as you move around and also might pull down a route to somewhere or a list of nearby pizza places.
So bottom line, you do NOT need data in all cases but your gps use is limited without data.