We\'re about to build a Blackberry application but would love some input on whether to implement using J2ME (MIDlet based) or Blackberry native (UIApplication).
There is a way in between: You could use J2ME-Polish and code natively in J2ME. Polish will add the look and feel of a native BlackBerry app to some extent. That has the advantage of porting your app to other J2ME phones and not be limited to BlackBerry.