Contacts initially created on a Samsung D900 phone and then synchronized using iSync may display a birthday of "January 1st, 1900" in Address Book.
By default, the Samsung D900 phone assigns an "empty" birthday to each new contact that's been created initially on the phone when synchronizing using iSync.
If you want a contact's birthday information to appear correctly, crate the contact in Address Book instead of on the phone device.
Important: Information about products not manufactured by Apple is provided for information purposes only and does not constitute Apple's recommendation or endorsement. Please contact the vendor for additional information.