maybe it is not new, what I just found out is you need customize, iphonebrowser, or ibrickr, and any .wav soundfile, you like to have as SMS sound.
In iphonebrowser goto VAR/root/cusomize/audiofiles
in here create a new folder, this folder will show up in customize, under sound,
Indeed of converting the wav file, just rename the exstension to .aif and drag it into the sound folder you created, now goto customize select it and you are done, you will not hear the sound when you select it, but it will work

hope I could help someone
