There is no blocking enforcement, yet. On Apple devices with some major carriers such as AT&T and Verizon, it provides a check mark beside a validated number (mostly, other mobile subscribers). The expansion of interoperability with the rest of US carriers, landline operators, and the international expansion will take years. And before blocking unsigned calls can happen, it will need to be phased-in and validated.

I stopped getting spam phone calls at least a year ago, so I presume something changed.