It will sync whatever contacts are on your computer: http://support.apple.com/kb/HT1296
To sync contacts with your computer, choose "Sync Contacts with" within iTunes for Windows, or "Sync Address Book Contacts" on your Mac.
You can sync your contacts with:
- Microsoft Outlook 2003, Microsoft Outlook 2007, Microsoft Outlook 2010 (Windows XP, Windows Vista, or Windows 7)
- Windows Address Book (Windows XP)
- Windows Contacts (Windows Vista / Windows 7)
- Address Book (Mac OS X)
- Microsoft Entourage 2004, Microsoft Entourage 2008, or Microsoft Outlook 2011 for Mac
Note: If using Microsoft Entourage, use Microsoft Entourage 2008 12.1.2 or later if syncing with Mac OS X v10.6 or later. If you would like to sync data on your Mac with Entourage, enable syncing between Entourage and Address Book.