I have just intsalled Mobie phone tools and the only sound files I can successfully play on the phone are midis. I can edit mp3s, I can transfer them but they will not play. You can do the editting by selecting the mulitmedia studio option when you bring up mobile phone tools itself. It's the one with the Bells icon.
Then select the Mp3 file you wish to edit. It's pretty obvious from there what to do.

If I figure out how to actually get the MP3 to play on the phone, I'll let you know.