Want to sync your iPhone across multiple computers? It’s a bit of a hassle, but here’s how to do it in iTunes 10. You may remember a while back we explained how to do it with older versions of iTunes.
This fix comes from MacRumors forums user fasttimes. According to the post it works on both Mac and PC. Here it is. (Note: We have not tried this one yet, so use at your own risk).
Please hit the jump to read the full tutorial.
1) Uninstall iTunes on all your extra machines, and delete everything in the directory that has the iTunes Music Library.XML and iTunes Library.itl files.
2) Install iTunes 9.2 (you can find it here)
3) Follow these steps:
Apple only allows you to sync your iPhone with one iTunes library at a time. When you attempt to sync your iPhone to another computer, you get the following message.
Note: “Computer 1″ represents your usual computer, “Computer 2″ represents the new computer you would like to sync your iPhone to.
On “Computer 2″, backup “iTunes Music Library.xml” and “iTunes Music Library” (Tunes Music Library on Windows) safely.
Download a Hex editor.
1. On Computer 1, open “iTunes Music Library.xml” with Notepad and search (Ctrl+F) for “<key>Library Persistent ID</key>”
2. Following “<key>Library Persistent ID</key>”, copy the code between <string> and </string>
In this example it is “8B6C633F7DACB74B”.
3. On computer 2, find that same code, and replace it with the code from computer 1.
4. Open “iTunes Music Library” (iTunes Library.itl on Windows) using your Hex Editor on computer 2.
5. In the Hex Editor, go to Edit > Replace.
6. In “Find”, insert code from computer 2. In “Replace With”, insert code from computer 1. There should be one match.
7. Save this file. Close it.
4) Unplug your iPhone.
5) Launch iTunes with auto-sync turned OFF
6) Plug in your iPhone again. Check your iPhone’s App page in iTunes. Check the “sync” checkbox and you should not see the message about removing your old apps.
7) Right click on the iPhone and transfer purchases.
8) Now you should be able to install iTunes 10 and sync both machines.
[Credit to fasttimes - Link]