Address Book has a cool feature that allows you to take multiple contacts and merge them into one, in case you accidentally have more than one copy, each with a different part of the contact’s information. (For example, one has their email and another has their cell phone number.)
To merge two contacts, simply highlight them and press Command-| (Shift + Backslash) or select “Merge Selected Cards” from the “Card” menu in the menu bar.

Alex Anastasiou
I have a client who merged every single contact in his address book into one contact. So now the single name in the address book has 200 numbers :(
I just wanted to know if you knew how to "unmerge" the contacts or if this is even possible.
Look forward to your reply
Kind regards
Alex Anastasiou
alex@eznetworks.co.za March 18th, 2008 at 6:33 am
Omer Zach
I don't believe Address Book has an unmerge feature, but if there is an intact contact list on another device (like an iPhone or iPod), you should be able to transfer them back over to the Mac and tell iTunes or iSync to overwrite from the device to the computer. March 18th, 2008 at 12:40 pm