To the best of my knowledge a MIDP .jar file is an MIDP .jar file. A friend of mine wrote an app using Eclipse, and it ran on his touchscreen Samsung. It also ran on my S60 series Nokia. I have written applications in Netbeans, and they have ran on a multitude of different phones. The prime consideration when thinking of running your application on different phones is the difference in screen resolution. However, a few lines of code will scale the application appropriately for the device it is being used on.
For the purposes of your application the easiest way to begin development is to download
Netbeans J2ME IDE.
Being an arrogant, arch-capitalist I have abandoned development on the J2ME platform in favour of the Android and iPhone platforms. (Apps == Money == :))