For the options under "Private Call Blocking"....

Block Private Calls - Blocks calls that are sent to us and flagged as private properly.

Block Unknown Calls - Blocks the above calls AND calls that do not have a name.

There is very little standardization in the industry. Some providers send the calls with a privacy to block the caller ID, but many VoIP providers don't this this...they just take the name out.

The block all unknown is the most strict and blocks anything regardless of the method they send it in. Before we added this, a lot of blocked calls from other VoIP providers were getting through.

If all carriers did things correctly and send the "privacy flag", this wouldn't be needed.