I've never made a game for a mobile so I'm not really sure what the proper convention for level info is. Basically I'm thinking that I include an xml file that I add to local diskspace for the app then load the level details (item positions, etc) from that xml file, this way when I have to update the game, add more levels, I only have the users download a small xml file. Is this method secure or are there other ways of doing this?
The security features on the BlackBerry can be pretty complicated, check out the second half of this article for a good summary of the various security features available:
http://programming4.us/mobile/2694.aspx
Here are some official BlackBerry docs on the topic too:
http://docs.blackberry.com/en/smartphone_users/deliverables/1487/Security_26381_11.jsp
FYI, most of this information concentrates on protecting data from unauthorized users, or from other malicious apps. Personally I wouldn't be too concerned about a sophisticated hacker changing my XML, unless I was giving away prizes for achievements!