This issue has already been discussed in the more recent posts in this thread amongst many others: http://www.blackberryforums.com/general-9000-series-discussion-bold/158487-howto-blackberry-maps-bold-t.html
AT&T caught on to the fun and put the kibosh on it a while back. The only way to get it to work standalone (not background through another app) is to restore your service books from a backup prior to the beginning of March. This will only work temporarily though, because as soon as service books are resent for any reason you will lose BB Maps again. You may just want to forget about it for now and go with Google Maps.
I'm not sure what the deal is with other carriers. They may just want to push their navigation apps on their customers like AT&T I suppose.