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 when a call is signed and is included in the STIR/SHAKEN call certificate. This attestation level establishes the relationship between the caller, the phone number, and the provider that enabled the call to enter the network. STIR/SHAKEN defines three 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 phone number. Attestation A indicates that the provider knows the caller’s identity and has verified authorization to use the number, which commonly occurs when the provider issued the number and the call originates on its own network. Attestation B indicates that the provider knows the customer but cannot confirm the right to use the specific phone number, which is common with third-party call centers using externally sourced numbers. Attestation C indicates that the provider is acting as a gateway and does not know the identity of the original caller, such as with calls entering from international networks. Attestation improves accountability and traceability by identifying which provider authorized a call and how confident that provider is in the caller’s identity and number usage. However, attestation does not determine whether a call is wanted and does not prevent calls from being labeled based on reputation, behavior, or consumer feedback. For enterprises, attestation is an important foundation but not a guarantee of call success. Even calls with full attestation can be labeled or ignored if number reputation issues exist. Strong call performance requires both authorization clarity and reputation protection. Numeracle supports this by helping enterprises and service providers manage identity, number authorization, and reputation alongside STIR/SHAKEN.

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.

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 when a call is signed and is included in the STIR/SHAKEN call certificate. This attestation level establishes the relationship between the caller, the phone number, and the provider that enabled the call to enter the network.

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The 3 Attestation Levels

STIR/SHAKEN defines three attestation levels labeled A, B, and C. Each level reflects how much the originating service provider knows about the caller and their right to use the phone number.

Attestation A, often called full attestation, indicates that the provider knows the caller’s identity and has verified that the caller is authorized to use the phone number. This commonly occurs when the provider issued the number and the call originates on its own network.

Attestation B, or partial attestation, indicates that the provider knows the customer but cannot confirm the customer’s right to use the specific phone number. This is common when third-party call centers or platforms originate calls using externally sourced numbers.

Attestation C, 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. This typically applies to calls entering the network from international gateways.

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What Attestation Establishes & Why it Matters

Attestation improves accountability and traceability across the voice ecosystem by making it clear which provider authorized a call and how confident they are in the caller’s identity and number usage.

However, attestation does not determine whether a call is wanted, nor does it prevent calls from being labeled based on reputation, behavior, or consumer feedback. Even calls with full attestation can be labeled or ignored if number reputation is poor.

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Attestation & Enterprise Call Performance

For enterprises, attestation is an important foundation for call authentication, but it is not sufficient on its own. Higher attestation does not guarantee better call outcomes if dialing practices, complaint rates, or number reputation create negative trust signals.

Enterprises benefit most when attestation is paired with clear number authorization, identity consistency, and active reputation management. This ensures that authenticated calls are not only verifiable, but also trusted and answered.

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.