Hm, no response yet :(

After reading this:
blackberryforums.com/developer-forum/23262-coding-vs-converting-blackberry.html (unfortunately I am not allowed to link, the board prevents it)

You "only" have to "convert" all the low level graphic operations, is this correct?

Helpful article from Sun: developers.sun.com/mobility/midp/articles/blackberrydev/