Both RVTraveller and I have been using our Blackberries with the Cacheberry application in conjunction with our Garmin Vista C GPS'rs for the past couple of years. Basically we use Cacheberry to get cache information as the Vista C only provides coordinates and limited info about the cache (name or hint etc when using GSAK). Yes it means two devices working but it beats paper caching.
I'm now on my second Blackberry as they don't stand up well to the wet coast environment
and so I decided to get Robyn a Oregon 500 with Canada Topo for Christmas. Now she has all the data (and loves it and me too
) that we need and my Blackberry can be "saved" for texting, call a geo-friend etc if we get really stuck at GZ.