iPhone sync with multipule computers.

Editor’s Note: The following article is an adapted excerpt from the recently-published Take Control of Your iPhone, a $15 electronic book available for download from TidBits Publishing. The 195-page ebook helps readers understand what’s going on under the hood of the iPhone, with lots of tips for using the iPhone more effectively and an emphasis on troubleshooting assistance for solving problems related to activating, syncing, application crashes, iPhone freezes, handset security, and more.

Although you can certainly sync multiple iPhones to a single computer, the reverse of that—syncing one iPhone to multiple computers, isn’t generally recommended by Apple.

Should you decide to ignore Apple’s advice and connect your iPhone to a secondary computer, don’t worry. Nothing is selected for syncing by default. That is, no contacts, calendars, music, video, or any other data will be selected in iTunes, so there will be no automatic syncing and no potential loss of data on either your iPhone or the computer.


If you click the Sync button, however, an initial sync does occur. Unlike with most iPods, no warning advises against this. Happily, it is still the case that no data are lost on either the iPhone or the secondary computer. All that happens is that an iPhone Backup file is created.

However, if you enable any of the checkboxes in the Info, Music, Photos, Podcasts, or Video tabs, the Apply button appears. If you click Apply, you do typically get a warning message. The exact content of the message, and what will happen if a sync occurs, varies depending upon what you selected. [Note: Although there are minor differences in the user interfaces, the iPhone and the iPod touch behave very similarly here.]

Music, video, and podcasts
If you enable syncing of music or video content (assuming you have previously synced music or video to your iPhone via the first computer), you get a message similar to the one in Figure 1.



Figure 1. This message appears when you set iTunes to sync music or video on a secondary computer (that is, a computer that isn’t the one you sync with normally).

If you continue with the sync, it will erase all the iTunes-specific content on your iPhone, replacing it with the content from the secondary computer, but leaving photos and info content (contacts, calendars, Mail accounts, and bookmarks) intact, despite the use of the word “erase” in the message. Any settings changes you made on the iPhone should remain intact as well.

If your iPhone contains songs purchased from the iTunes Music Store and you connect to a secondary computer that is authorized to play music from your account, the message in Figure 1 includes an additional button to “Transfer Purchases.” See this Apple article for details.

Oddly, at least on recent iterations of the iPhone software, the above warning message does not appear when you attempt to sync podcasts from the secondary computer—even though podcasts are also part of an iTunes library. Instead, either no message appears or a message appears that states that only podcasts will be affected by your sync. In either case, if you go ahead and sync, you’ll get the same result: the newly selected podcast(s) replace the podcasts currently on your iPhone—while the music and video media on your iPhone remain unchanged and intact. I am not sure why podcasts are an exception here, but they are.

Photos
If you enable photo syncing on the secondary computer, you get a message like the one in Figure 2. If you go ahead with the sync, all photos on the iPhone will be replaced, but all non-photo content should remain untouched.



Figure 2. This message appears when you set iTunes to sync photos on a computer different from the one with which you normally sync.

Contacts, calendar events, Mail accounts, and bookmarks
If you tell iTunes to sync any of these types of data and click Apply, you get a message like the one shown in Figure 3.



Figure 3. This message appears when you set iTunes to sync iPhone’s contacts on a computer different from the one with which you normally sync.

In this special case, you can choose to merge information between the iPhone and the second computer rather than overwrite the synced data on the iPhone. The merged data, now on your iPhone, would then sync back to your main computer the next time you sync with it. Thus, this allows you to combine all the types of information managed on the Info tab (contacts, calendar events, Mail accounts, and bookmarks) in multiple computers.

Merging of Info data is the one case where syncing with a second computer can be useful. You can use the iPhone as a means of merging two sets of data from separate computers.

In all other cases, syncing an iPhone with a second computer results in data from the second computer overwriting similar data from the first computer, which is not typically what you want. However, if you had an unusual setup where you wanted, for example, to sync your iPhone to one computer for photos and to another for music, syncing to both computers could accomplish this. To do so, sync photos but not music on one computer, and vice versa on the second. Keep all other settings and content synced with just the first computer.

Sync to More Than One iTunes Library
How would you like to be able to sync music, video, and pod-casts from a second computer to your iPhone, without erasing the content from the first computer that is already on your iPhone? It can be done, but only if you have a "jailbroken" (hacked) iPhone. If so, install SwapTunes via the Installer application on your iPhone.

The only other option is to manually combine the content from multiple computers into a single iTunes Library, on one computer, with which you sync your iPhone.