use fugu or simular program to sftp into your iphone.
then got to folder var/ringtones (on 1.1.2 or earlier)
1.1.3 an 1.1. 4 its library/ringtones
and simply drag them into that folder.
just make sure they are .m4r
for msg tones on 1.1.4 change your chosen sound file exstention to .caf (you should simply b able to rename it.)
change the file name to sms-received(any no. 1-6).caf
put it in folder system/library/audio/uisounds
and click replace.
you msg tone will now be there but it will have the name of the iphone original tone but it will still work.
i have not tested how long msg tones can be so if someone fancies testing please post so i can add it to this post.
please give rep if you think its due