PhoneAble
About
Normally an iPhone is associated with just one iTunes library, and you can only manage your music with that one copy of iTunes. PhoneAble takes your iPhone library key and applies it to any number of other iTunes installations, allowing you to manage your music on whatever computer you happen to be at. It's pretty easy to use:

Initially your iPhone is synced with the first computer you use it with. When you plug it into a second computer you can't sync or manage the music on the phone. PhoneAble allows you to manage your music manually on the 2nd computer, which is different to syncing your music. You can still only sync music on the first computer.

1) On the second computer, plug your iPhone in, and back it up by right clicking on the device in iTunes and selecting backup.
2) Now close iTunes and run PhoneAble, run through the steps.
3) Open iTunes again, click on the phone in the devices section, then on the summary tab there is an option "Manually manage music and videos", make sure that is on and Apply the change. Now try and drop some music files on the iPhone device, it should now allow you to copy music to your own phone.

iTunes 10
Note: PhoneAble is not currently compatible with iTunes v10. The problem is that after PhoneAble sets the library key in iTunes config files, iTunes replaces the keys with the key it generated from somewhere else. I'm currently looking into the issue. So far I can't find where else it's storing the Library Key. (16/9/2010)
Note: The mac port is still in the process of being tested, there is a alpha release if you are dying to try it but it may not work as expected. And don't blame me if it destroys your iTunes config.
Download And History
1.3 [Stable]
Download: Installer [Windows, 210K, 22/8/2010]

Changes:
  • Added a lot of logging, improved error messages.
1.2 [Beta]
Download: Installer [Windows, 209K, 12/8/2010]
1.1 [Beta]
1.0 [Beta]
Other Links