The bottom line (at least so far), if you have a Java program that you want to be able to run on the MPx220, you have to:
1) Make sure there is a jad file, in addition to the jar file. (if not, it won't work)
2) Download the JAD file onto the phone using IE.
(Unfortunately, this means if you have java files on you PC, or elsewhere, you have to get them posted on a web server someplace to be able to install them on the phone, and yes this is ridiculous, but it's the only way I have been successful thus far. The jar file has to be there (on the web server) as well, but you must select the jad file (from IE) to get it to setup on the phone)
I think there are tools out there that can make a jad file from the jar file. I'll have to look around (maybe this weekend) and get back to you.
As a test, I would recommend going to the site:
http://midlet.org/index2.jsp
(it has free Java Programs)
Use that site and download a jad file from there, just to be sure you can do it. If you want, take a look at the site with your PC first (just to get familiar with it), but in the end you will need to use your phone to connect to the site using IE (on the phone), and then select a jad file on that site (midlet.org).
IE will launch the Java Setup program and you will get a few dialog boxes prompting you whether you want to install it or not.
Here is one I loaded that runs on my phone "WebGate Chess" at this URL:
http://midlet.org/repository/webgate/wgche...ess/wgchess.jad
Or you can go to the web page it is on and scroll down a ways to find it, as there are several on that page.
http://midlet.org/category.jsp?parentLevel=82
Hope this helps.