iTunes insists on erasing my iPhone I have an iPhone that was synced to an iTunes library. Then I upgraded my Mac, and forgot to backup the iTunes library and transfer it to the new Mac. Ever since, I have been manually managing my music by dragging and dropping it from the filesystem onto iTunes, and not "syncing".

And things have been working fine for the past few years. But now, after yet another Mac upgrade, and upgrading to iTunes 11, I can no longer manually manage my music on my iPhone. When I try to turn on "manually manage music and videos", iTunes says:

The iPhone “kPhone” is synced with another iTunes library on “kart's macbook”. Do you want to erase this iPhone and sync with this iTunes library?

I don't want to erase the whole phone -- apps, app data, app settings, synced data in apps, videos, books, etc. I just want to copy music onto the iPhone. I have already deleted the music that's already on the iPhone. How do I copy music?
I just ran into the same problem. Here's the solution:

There are "iPhone Managers" that Apple does not promote using but it works 100%. These "iPhone Managers" (the names I'll give you in a second) allow you to transfer your CONTACTS, MUSIC, APPS, APP DATA, APP SETTINGS, PHOTOS &amp; VIDEOS and a LOT more to your Mac or Windows computer. 

After you transfer whatever it is you want to keep a backup of to your Mac in a nicely labeled folder on your desktop (just in case the iTunes Manual Backup doesn't keep some of your settings or pictures, contacts, etc.), you can then ERASE AND SYNC and transfer everything from the folder you made on your desktop with all of your files and transfer it back.

This is the only way I know and am doing it as we speak.

I tried posting links but since I'm new it won't let me. You can try these names:


CopyTrans
iFunBox for Mac
FileApp


I hope this helps.