Symptom
A contact's last name and first name both appear in the Last name field in Address Book.
Solution
On some phones, you can set contacts to be displayed by either last name first or first name first. If the phone is set to display contacts with the last name first, the contact name will be reported to iSync incorrectly, and it will sync erroneous data into Address Book. Consult the documentation that came with your mobile phone, or contact the phone's manufacturer for more information about how to set the sync view to First name Last name.
Related document
302470: "
iSync: First and last name fields show up as dots or dashes on phone"