STIR/SHAKEN Explained: Attestation, Spam Labels and Answered Calls

Your client’s office calls back a warm lead. The lead’s phone lights up with “Spam Likely,” and they decline without a second thought. The client blames the lead list. The real problem is that their calls look untrustworthy to the phone network.

STIR/SHAKEN is a big part of how that trust is decided. If your agency sets up phone numbers, dialers, or AI agents for clients, you should understand what it is, what it isn’t, and which parts you can influence.

This article is general information, accurate to our understanding as of 2026. It is not legal advice. FCC rules and carrier practices change, so check current requirements with your telephony provider.

The problem STIR/SHAKEN tries to solve

For decades, caller ID was easy to fake. A robocaller could display any number, including a local number or a well-known business. That made people stop answering unknown calls, which hurt every legitimate business that relies on the phone.

STIR/SHAKEN is a set of technical standards that lets phone carriers digitally sign calls and verify that signature on the other end. The names stand for:

• STIR: Secure Telephone Identity Revisited
• SHAKEN: the companion framework that defines how carriers sign, pass along and verify that identity information between networks

You don’t need to remember the acronyms. The idea is simple: the carrier that starts a call vouches for whether the caller is allowed to use the number shown, and the carrier that delivers the call checks that promise.

In the US, the FCC requires voice providers to implement STIR/SHAKEN on their IP networks and to take other robocall mitigation steps.

How it works, step by step

1. A call starts. Your client places a call through their provider, such as a Twilio-connected phone system.
2. The originating provider signs it. The provider adds a digital signature to the call that includes an attestation level (explained below).
3. The call travels across networks. The signature goes along with the call on IP networks.
4. The terminating carrier verifies it. The recipient’s carrier checks the signature.
5. Analytics decide the display. The carrier combines the verification result with its own call analytics to decide how to show the call: normal caller ID, a verified indicator, or a warning label.

That last step matters. STIR/SHAKEN is one input. Carrier analytics, based on call patterns and complaints, often decide whether a “Spam Likely” label appears.

Attestation levels explained

The originating provider assigns one of three levels.

Level	Name	What it means
A	Full attestation	The provider knows the customer and confirms they’re authorized to use the calling number
B	Partial attestation	The provider knows the customer but can’t confirm they’re authorized to use this specific number
C	Gateway attestation	The provider is passing the call along but can’t vouch for the source

For your clients, the goal is A-level attestation. It’s the strongest signal that the call is legitimate. It usually requires that the number belongs to the business’s account with the provider and that the business has been verified.

What STIR/SHAKEN does not do

A few common misunderstandings cause confusion with clients:

• It doesn’t block calls by itself. It authenticates caller ID. Blocking and labeling come from carrier analytics and apps.
• A-level attestation doesn’t guarantee no spam label. If a number makes many short, unanswered calls, analytics may still flag it.
• It doesn’t display your business name. Branded caller ID is a separate service, though it often builds on verified identity.
• It doesn’t fix bad calling practices. Calling people who never asked to hear from you will hurt reputation no matter how well your calls are signed.

Why this matters specifically for agencies

Agencies often set up phone systems for many clients at once. That creates a few risks:

• Shared or mismatched numbers. Using one number across multiple clients, or calling from numbers not owned in the client’s account, can weaken attestation.
• High-volume outbound. Power dialers and outbound campaigns create patterns analytics engines watch closely.
• Unverified accounts. Skipping business profile verification with the telephony provider can mean weaker attestation.
• Client blame. When calls go unanswered, clients may blame your leads or your campaigns.

Getting STIR/SHAKEN and reputation right protects your results and your reputation.

Example: a solar installer with a spam label problem

Clearsky Solar Co. is an invented residential solar installer working with an invented agency, Redwood & Rail Marketing. Clearsky’s reps called back web leads from a single number. Answer rates dropped over a few weeks, and several leads told reps their calls showed as “Spam Likely.”

Redwood & Rail worked through the issue:

1. Verified the business. They completed the business profile and trust verification steps in the client’s telephony provider account, so calls could be signed with stronger attestation.
2. Checked number ownership. All outbound numbers were confirmed as owned in Clearsky’s own account.
3. Reviewed calling patterns. Reps were calling every lead up to five times in two days. They reduced this and spaced attempts out.
4. Led with text. New leads now receive a text first, so they recognize the number when the call comes.
5. Registered numbers with reputation services. They used free carrier and analytics registration portals to register the business numbers and dispute incorrect labels.
6. Monitored answer rates. They tracked answer rate by number weekly to catch problems early.

The spam labels didn’t vanish overnight, but answer rates improved as call patterns normalized. Just as importantly, Clearsky now understood why it happened.

Practical checklist for agencies

Use this checklist when setting up phone systems for clients:

• Keep each client’s numbers in their own account. Don’t share numbers across businesses.
• Complete business verification with the telephony provider. With Twilio, this typically means setting up a business profile and enabling trusted calling features.
• Call from numbers the business owns. Avoid displaying numbers you can’t prove the business is authorized to use.
• Use local numbers that match the service area. They look familiar and support callbacks.
• Pace outbound calling. Avoid bursts of short, unanswered calls from one number.
• Warm up contact with a text when you have consent to text.
• Register numbers with major carrier and analytics registration portals, and check labels periodically.
• Honor do-not-call requests promptly and keep internal do-not-call lists.
• Monitor answer rates and investigate sudden drops.

SaaSVisionary’s phone system runs on your own connected Twilio account, which means verification and number ownership live under the business’s own profile. Power dialer features are available on the Team plan and above, so pacing and list hygiene become especially important there.

STIR/SHAKEN and AI calling

AI phone agents that place outbound calls are subject to the same caller ID framework. They also face additional rules. The FCC has taken the position that AI-generated voices count as “artificial” voices under the TCPA, which affects consent requirements for certain calls. If your agency plans to use outbound AI calls, treat consent and disclosure as part of the setup, not an afterthought. Our article on AI phone agents and lead qualification covers the inbound side, which is the easier place to start.

Key takeaways

• STIR/SHAKEN lets carriers sign and verify calls so caller ID can be trusted.
• Attestation levels A, B, and C show how strongly the provider vouches for the caller. Aim for A.
• It doesn’t block calls or remove spam labels by itself; carrier analytics also play a big role.
• Verify each client’s business with the provider, keep numbers separated, and pace outbound calls.
• This is general information as of 2026, not legal advice.

FAQ

Does STIR/SHAKEN stop my calls from being labeled “Spam Likely”?

Not on its own. STIR/SHAKEN verifies that caller ID isn’t spoofed. Spam labels are applied by carrier analytics based on call patterns, complaints, and other signals. Strong attestation helps, but you also need healthy calling behavior, registered numbers, and consent-based outreach.

How do I get A-level attestation for my clients’ calls?

Typically, the business must be verified with its telephony provider, and calls must come from numbers owned in that business’s account. With providers like Twilio, this involves completing a business profile and trusted calling setup. Exact steps vary by provider, so follow their current documentation.

Is STIR/SHAKEN used for SMS as well?

No. STIR/SHAKEN covers voice calls. Business text messaging in the US is governed by different systems, mainly A2P 10DLC registration for local numbers and separate verification for toll-free numbers and short codes.

Can an agency use one phone number for several clients?

It’s a bad idea. Sharing numbers blurs who is actually calling, can weaken attestation, and mixes reputations so one client’s calling habits affect another’s. Give each client their own numbers in their own account.

Is branded caller ID the same as STIR/SHAKEN?

No. Branded caller ID shows a business name, and sometimes a logo, on the recipient’s screen. It is a separate service offered by carriers and third parties. It often relies on verified identity, so good STIR/SHAKEN practice supports it, but they are different things.