I'm currently manually managing music on my iPhone 4, but I want to be able to automatically sync books, ringtones, etc., and bizarrely this means I have to do the same with music. I ran into the same problem on an iPad 2 a couple of weeks ago and found that when I checked "Sync Music" and asked it to sync selected music, it actually kept all of my music and automatically checked the artists, albums, etc. which I'd added manually. Any songs which I didn't upload in a full album were added in a "manually manage" window at the bottom of the music sync screen. I can't, however, figure out how to do the same on my iPhone. Any time I click "Sync Music," it threatens to erase all of my music. Does anyone know how to reproduce this? I stumbled upon it by accident (on my second try) with the iPad.