I can tell you that MP3 uploads to a v600 work well.  An MP3 shows up in
the Sounds file and you just press Play to hear it.  I converted a wav
file using the Ease MP3/Wav Converter (www.audiotool.net) and then
uploaded the MP3 file to the v600 using Mobile Phone Tools 2.0.
 A note about wav to MP3 converters. There are dozens of them
available. I spent the better part of yesterday trying some of them.
Some sounded terrible, some worked but added pops and clicks, others
sounded good but wouldn't upload to the phone or would upload and
produce an error message on playback.
The Ease product, which is shareware, was about the 8th one I tried. It
was intuitively easy to use and  produced an MP3 true to the wav file
and uploaded to the phone easily.  Playback, obviously, was successful
and I now have a cool new ringtone.  Do a google for flintphone.wav
(note: there are several and the quality varies) and see if you like it.
If anybody would just like the mp3 let me know.

From:Lee
barlow2000@NOSPAMbarlow2000.karoo.co.uk

Yes, it is, I've sent mp3 tones to my email address & then collected the
email via my phone. It asks if you want to save the attachment and/or set as
ring tone.
Don't know about .jar files though.