Call Attestation (A, B, C)

Call attestation is the level of confidence a phone carrier signs onto a call under STIR/SHAKEN about who is calling and whether they may use the number shown.

When a call starts on an IP network that uses STIR/SHAKEN, the originating carrier adds a digital signature. Inside that signature is an attestation level. It tells the receiving carrier how much the originating carrier knows.

• A, full attestation: the carrier has a direct relationship with the caller and has confirmed the caller is authorized to use that phone number.
• B, partial attestation: the carrier knows the customer who placed the call but cannot confirm they are authorized to use the number shown.
• C, gateway attestation: the carrier received the call from somewhere else, often an international or non-signing network, and cannot vouch for the source.

Attestation is decided by your phone provider. You cannot buy A attestation as an add-on. You earn it by having your business verified with the provider and by calling from numbers your provider has assigned to you or confirmed you are allowed to use.

A attestation does not guarantee that a call will be answered or that it will avoid a spam label. Carriers and analytics firms look at many signals, such as complaint rates and calling patterns. Still, low attestation on legitimate calls is worth fixing. If you are unsure what level your calls receive, ask your provider directly. Many will tell you or show it in call logs.

Sources

• FCC, Combating Spoofed Robocalls with Caller ID Authentication: https://www.fcc.gov/call-authentication (accessed October 17, 2026)

This entry is general information, not legal advice.