I don’t think the cameras are “calling home”. I monitored the network packets being exchanged. The cameras are sending “Keep Alive” messages to the server, right after powering up. This means, they are always connected, unless of course the there’s a network failure.
If always connected, they don’t need to “call home”. What I understand happening during authentication (unverified), is that the client (phone/tablet/etc) is checking with the camera if the id/passwords are correct.
And I discovered by chance that if you have local SD recording enabled, it’s also checking the SD card. It tries to access it during authentication. This explains why a few here have posted that removing the SD cards (that likely failed) “fixed” their authentication issues.