Google Maps is the only app that uses towers for triangulation. In my experience it it will not do much more than give you a very general idea of where you are...you should not expect tower triangulation to be very usable for navigation purposes.

The Freedom Keychain 2000 GPS is the best small GPS puck I've seen...I bought one and use it w/my Pearl and love it. There's a thread on it here:

http://www.blackberryforums.com/bbf-...-receiver.html

In the GPS forum there is a thread on the Mapquest navigation software...free, turn-by-turn voice directions.