This service is free and works with Caller ID service. Anonymous Call Rejection would reject any incoming call from an anonymous location (any caller whose name and number would not show up on your Caller ID display). The rejected caller would be instructed that the location does not accept anonymous calls and how to allow the call to go through by identifying themselves. The service will reject ALL calls that are not identified by name and number, so there is the potential of missing calls you may want to receive.