The jar file needs to be converted into a .cod file, which runs on blackberry. Apparently, there are three ways of doing this.
* Antenna, an open source ant based project.
* Blackberry's enterprise server, which, from what I've read, converts jar files to cod files on the fly.
* Recompiling the code (or importing the jar? not sure here) in the IDE.
I assume you have a blackberry device? If so, you can try just using the antenna
wtkrapc task. I'm trying to avoid the IDE, and there doesn't seem to be a way to load the simulator apart from the IDE. But I can generate a .cod file using this task.
The jad file also definitely needs to change. See the "deploy .cod files" section of the BlackBerry_Developer_Guide_Volume_1_-_Fundamentals.pdf available at the RIM website for additional attributes needed in the jad file. (Unless you're using the Mobile Data Service of the Blackberry Enterprise Server, in which case magic seems to happen? Not sure.)
However, I don't believe any code changes have to be implemented, since I believe that the Blackberry implements all of MIDP 1.0. See the document titled Creating_MIDP_Applications.pdf for more info.