Q: My wife and I each have iPhones and I’m worried about losing contacts from one or the other when I enable iCloud. How does the syncing work? For example, if we have the same names in our contacts list, but the information is different (mine is not as complete, for example), then is there the chance that information will be lost when they are synched? Or, is is strictly an additive type sync?
A: iOS 5 will do its best to prevent data loss. Merging two different contact lists into a single iCloud account will try to match up what contacts it can and merge the information, but more commonly you will simply end up with duplicate contacts where the information cannot be reconciled. You will then have to go through your contact list later and resolve these yourself.
If you’re using Mac OS X, the built-in Address Book application provides a feature for manually merging address book cards, allowing you to review each as you go through the process.
You may want to consider simply setting up each device for its own iCloud account. You and your wife can then store your own contacts, calendars and other data separately, If you want to share some features of iCloud (e.g. Photo Stream), you can do this by setting up a third iCloud account to share that data, or simply having one of you share the other’s account for common information while using a separate account for personal info.
You can even enable contacts on more than one iCloud account on your device to access and sync contacts from both accounts—the Contacts app will provide a unified contact view for any contacts that exist in both accounts, displaying them as a single contact with combined information from both.
The only thing to keep in mind here is that only the primary iCloud account on each device can be used for Photo Stream, Documents & Data and iCloud Backups, so if you want to share any one of these features, you’ll end up having to share all of them. However, the other iCloud services such as Mail, Contacts, Calendars, Reminders, Bookmarks, Notes and Find My iPhone can be disabled for the primary account and then configured in a secondary iCloud account. Our recent article on the Secrets and Features of iCloud discussed how this works in more detail.