I had previously patched the check out in the MusicLibrary binary, and forgot to write it up. However, I just looked at it again, and it turns out that you can get it to work just by changing a simple XML file. I guess they didn’t really care if jailbroken iPhone users used third-party software.

Here’s how: Edit /System/Library/Lockdown/Checkpoint.xml, find the DBVersion key, and change its value from 4 to 2. Save and reboot. Voila! I haven’t tested this extensively, but it seems to work at least on 2.1 and 2.2. You can then use Amarok or any other libgpod app to transfer data to the device (using the usual sshfs mount trick which is documented elsewhere for 1.x iPhones)

Update: abu from ml_ipod pointed out that DBVersion 3 also works. This version includes the old hash which was already present in older versions. I have tested this to work on version 2.1 of the iPhone software.
Update 2: DBVersion 3 works only on some devices, better stick with DBVersion 2.

MobileMusicPlayer synced via Amarok