Quoth Patrick O'Callaghan on Sweetmorn, the 54th of The Aftermath:
Alternatively, you could jailbreak the phone and copy files using
scp. I don't know if the phone will then recognize them as something
it can play, but I wouldn't bet on it.
I was able to use gtkpod[1] on a jailbroken iphone to transfer music,
manage playlists, photos, etc.
Footnotes:
[1]
http://www.gtkpod.org/about.html