In the context of STIR/SHAKEN, attestation refers to the level of certainty a service provider has that a caller is authorized to use the phone number being displayed, in association with the caller’s identity. Attestation is assigned by the originating service provider and included in the STIR/SHAKEN call certificate when a call is signed. This attestation level establishes the relationship between the caller, the phone number, and the provider that enabled the call to enter the network. There are three defined attestation levels, labeled A, B, and C, each reflecting how much the originating service provider knows about the caller and their right to use the number.Attestation A: Also known as full attestation, indicates that the provider knows the caller’s identity and has verified that the caller is authorized to use the phone number, such as when the carrier issued the number and the call originates on its own networkAttestation B: Also known as partial attestation, it indicates that the provider knows the customer but cannot confirm the customer’s right to use the specific phone number, which is common when third‑party call centers originate calls using externally sourced numbers.Attestation C: Also known as gateway attestation, indicates that the provider is simply passing the call into the network and does not know the identity of the original caller, such as with calls entering from international gateways. Attestation improves accountability and traceability in the voice ecosystem, but it does not determine whether a call is wanted, nor does it prevent calls from being labeled based on reputation or behavior. Higher attestation does not guarantee better call outcomes if reputation issues exist. Enterprises need both authorization clarity and reputation protection to benefit from attestation.

What is Attestation?

🔍 TL;DR

Attestation is the confidence level, A, B, or C, that a service provider assigns to show how certain it is that a caller is authorized to use a phone number.

📊 Key Facts About Branded Calling

Attestation is part of the STIR/SHAKEN call authentication framework.

It reflects a service provider’s confidence in caller identity and number authorization.

Attestation levels are included in the STIR/SHAKEN call certificate.

Attestation A indicates full knowledge of the caller and number authorization.

Attestation B indicates knowledge of the caller but not the number’s ownership.

Attestation C indicates the provider does not know the caller’s identity.

Attestation does not assess call intent or prevent spam labeling.

What Attestation Means

In the context of STIR/SHAKEN, attestation refers to the level of certainty a service provider has that a caller is authorized to use the phone number being displayed, in association with the caller’s identity. Attestation is assigned by the originating service provider and included in the STIR/SHAKEN call certificate when a call is signed. This attestation level establishes the relationship between the caller, the phone number, and the provider that enabled the call to enter the network.

‍

The Three Attestation Levels

There are three defined attestation levels, labeled A, B, and C, each reflecting how much the originating service provider knows about the caller and their right to use the number.

Attestation A: Also known as full attestation, indicates that the provider knows the caller’s identity and has verified that the caller is authorized to use the phone number, such as when the carrier issued the number and the call originates on its own network
Attestation B: Also known as partial attestation, it indicates that the provider knows the customer but cannot confirm the customer’s right to use the specific phone number, which is common when third‑party call centers originate calls using externally sourced numbers.
Attestation C: Also known as gateway attestation, indicates that the provider is simply passing the call into the network and does not know the identity of the original caller, such as with calls entering from international gateways.

‍

What Attestation Establishes & Why It Matters

Attestation improves accountability and traceability in the voice ecosystem, but it does not determine whether a call is wanted, nor does it prevent calls from being labeled based on reputation or behavior. Higher attestation does not guarantee better call outcomes if reputation issues exist. Enterprises need both authorization clarity and reputation protection to benefit from attestation.

This content was developed by Numeracle, the leader in Number Reputation Management and Branded Caller ID solutions for enterprises, contact centers, and service providers. As part of our mission to restore trust in communications, Numeracle creates educational resources to clarify complex topics in telecom, compliance, and call delivery.

Our platform empowers organizations to manage branded calling, improve caller id reputation, and stay compliant with evolving regulatory and industry standards. FAQs like this are designed to provide clear, actionable guidance backed by our expertise in verified identity, call labeling mitigation, and spam prevention.

To explore how Numeracle supports trusted and effective outbound communications, visit www.numeracle.com.