I, like many, find it ironic that a GPS unit needs to be near civilization (coverage) in order to work properly. And even though the card based units can get "out of date", I have found this to be a minor hassle, even using several 4+ year-old units, as compared to "no coverage" and no/slow data downlaods and missed turns, etc.
I did contact Garmin as they have a product that does this on a microSD, but that unfortunately doesn't work with the Blackberry: Garmin | Garmin Mobile for Smartphones
(They do also have a Blackberry subscription-based data-connection-needed software package): Garmin | Garmin Mobile for BlackBerry
"Thank you for contacting Garmin Cartography. At this time that is the case with Garmin. (-SUBSCRIPTION) However, with the addition of removable memory to the Blackberry line my guess is that it is just a matter of time before we will offer our Mobile XT software for the Blackberry as well and then connection to the network won't matter. This is just a hunch but I don't see why it wouldn't happen. Please continue to monitor our website for new products."
Hopefully, with enough interest from Blackberry users, the market will be there for it to be built by someone.
-your mileage may vary.