*.jar -file is necessary but *-jad file makes it very easy to download application from website. Just upload your jad & jar to the website (should save to same folder) and then browse with WAP to that site...
Like: http://www.something.com/YourMidlet.jad
6600 loads automatically jad-file and then you have chance to download the "real application" ie. *.jar. It is installed automatically to phone.