The highest attestation, 'A', is granted to customers who use a Plivo-rented US Direct Inward Dialing number (DID) as the caller ID for making outbound calls to the US. You can easily rent a US DID through our API or console.
Additionally, you can obtain a 'B' attestation for calls made using a verified US caller ID. You can verify your US numbers within Plivo's system using the Verified Caller ID API or console.