Yes, but we don't even have to go that far: international != unattested. Legitimate overseas telecoms should be able to sign their communications. The point isn't to seal off the USA, the point is to have someone to ban if they start abusing access.
Most international telecom operations aren't facilitating scam call centers, and of the ones who are I suspect very few are so eager to turn a blind eye that they will continue to do so when staring down the barrel of actual consequences.
Most international telecom operations aren't facilitating scam call centers, and of the ones who are I suspect very few are so eager to turn a blind eye that they will continue to do so when staring down the barrel of actual consequences.