Can you use MacOS Contacts with CLINQ MacOS?

Unfortunately, No, not at the moment. We are working on this, but currently do not have any timeframe as to when this can be expected.

Can you use iOS Contacts with CLINQ iOS?

Yes. CLINQ iOS uses iOS CallKit to be able to obtain access to the local Contacts and these are then displayed in the CLINQ Call History. 

Privacy iOS Contacts:
The contacts are loaded locally via CallKit.

Contacts are saved locally in the CLINQ app, so that the contacts do not have to be loaded completely anew when starting the CLINQ iOS App. Depending on the number of contacts it could otherwise lead to a wait-time of several minutes where the CLINQ call list would only display phone numbers without the "name" information.