Syncing with Apple Contacts
You can sync BusyContacts with Apple Contacts on your Mac.
BusyContacts can sync with the built-in Contacts app on OS X through a cloud-based service (iCloud, Exchange, Fruux, Google, or a CardDAV server). If OS X Contacts is already syncing with a cloud-based service, it should automatically sync with BusyContacts once you've configured BusyContacts to sync with the same account.
BusyContacts will not sync local "On My Mac" contacts with OS X Contacts. The Setup Assistant will allow you to import local contacts from OS X Contacts, if they exist, but this is a one-time operation and the local contacts will not remain in sync between BusyContacts and OS X Contacts.