Unless you’re using over-the-air Microsoft Exchange syncing with your iPhone (via Google Mobile Sync, NuevaSync or a corporate Exchange server), you’re probably keeping its contact and calendar information in sync with Outlook or iCal using iTunes.
This works well enough, but what if your calendar and contact data is stored one computer (at the office, say) and your iTunes library is stored on another (maybe at home)? Try plugging the iPhone into both and you’ll quickly discover that iTunes is fond of erasing the data put in place by the other iTunes on every sync.
Fortunately, you can successfully synchronise an iPhone or iPod Touch with iTunes on two separate computers — here’s how.
NB: I’ve assumed that you’re starting with the computer that contains your contact and calendar info — if not, just start at step 5 and flip everything around. It should be clear enough if you read through all the steps first.
Connect your iPhone or iPod Touch to your computer and, if it doesn’t open automatically, start iTunes. If iTunes starts synchronising, cancel it (it doesn’t matter if you don’t, but the sync is redundant at this stage). Select the iPhone in the Devices list, the click the Summary tab in the right-hand pane. Disable the ‘Automatically sync when this…’ option for now, then click Apply.
Click the Info tab and enable Contacts and/or Calendar syncing, then click Apply.
Click the Music tab and disable ‘Sync music’. It’s worth noting that this computer should not contain any music or playlists — if it does, this sync set-up won’t work properly, as you can’t sync two music libraries at once. Click Apply and disable the sync options for everything else you don’t want to sync on this computer.
That’s it for this computer, so click the Sync button and wait while iTunes synchronise your Calendar and Contacts info, plus anything else you elected to synchronise. If iTunes pops up a warning about this iPhone already being synced with another user account, click the Replace Info button to overwrite the iPhone with this computer’s data, or the Merge Info button if you want to combine the data on the iPhone with that on the computer. As a final step, re-enable the ‘Automatically sync…’ option on the Summary tab.
Now on to the computer that contains your music library (and anything else you want to sync). Essentially, you just need to repeat the first four steps, but deselect every sync option you selected on the other computer. Just remember that you can’t sync the same data on two computers, so the two iTunes sync configurations should complement each other.