What STIR/SHAKEN Means for B2B Outbound Teams in the US and Canada

What STIR/SHAKEN is

STIR/SHAKEN stands for Secure Telephone Identity Revisited (STIR) and Signature-based Handling of Asserted information using toKENs (SHAKEN). It is a framework for cryptographically signing outbound calls to verify that the calling number has not been spoofed.

In practical terms: when your SIP carrier places a call to a US or Canadian number, it attaches a PASSporT (Personal ASSertion Token) to the SIP INVITE. This token includes the calling number, the called number, and an attestation level. The terminating carrier reads the token and uses it as one input into its spam-scoring algorithms.

The FCC mandated STIR/SHAKEN implementation for US originating carriers by June 2021 for large carriers. Canada followed with similar requirements. The framework is not optional for compliant US/CA SIP carriers — it is a regulatory requirement.

The three attestation levels

STIR/SHAKEN defines three attestation levels, and the level assigned to your calls depends on your carrier's relationship with the number being used:

Full attestation (A): The carrier has verified the calling party's identity and that they are authorized to use the calling number. This is the strongest attestation and the one that terminating carriers treat most favorably. It requires the originating carrier to have a direct, verified relationship between the customer and the specific number being used.

Partial attestation (B): The carrier has verified the customer's identity but cannot confirm the customer is authorized to use the specific calling number. This occurs in scenarios where a customer is presenting a number that was ported from another carrier.

Gateway attestation (C): The call has entered the US/CA PSTN from an international network, and the originating carrier cannot attest to either the customer's identity or their authorization to use the calling number. International calls without proper STIR/SHAKEN origination receive C attestation at the US gateway.

For outbound sales teams, Full (A) attestation is the target. Numbers provisioned directly through UnlimCall's network for your account — not ported in from another carrier — receive Full attestation on US/CA outbound calls. The call carries a verifiable, cryptographic signature that the number is legitimately associated with your account.

What STIR/SHAKEN does not do

STIR/SHAKEN does not guarantee your calls will not be flagged as spam. It is not a whitelist. It is not a reputation guarantee.

What it does is provide a data point to terminating carrier analytics systems. A call with Full (A) attestation says: this originating carrier has verified this customer is authorized to use this number. It does not say: this call is not spam. A STIR/SHAKEN-attested call from a number associated with aggressive outbound behavior can still be flagged by analytics providers like STIR/SHAKEN attestation and spam flag status are separate signals evaluated independently.

STIR/SHAKEN reduces the risk of your call being flagged as "Spoofed" — calls where the calling number has no verified relationship with the originating carrier. It is most protective against spoofing-flag risk, not general spam-flag risk.

Why attestation level matters for B2B outbound

For a B2B outbound team calling US and Canadian prospects, Full (A) attestation on every call has two practical benefits:

Reduced likelihood of a "Spoofed" or "Scam Likely" label. Terminating carriers assign these labels based on multiple signals. An unattested call — or a call with Gateway (C) attestation — contributes more to a negative label risk than a Full-attested call. The distinction matters most for high-volume outbound, where calls from the same number reach many prospects in a short window.

A foundation for consistent caller ID presentation. Full attestation requires a verified relationship between your account and the specific number. That relationship is the same requirement that enables consistent, non-rotating caller ID provisioning. UnlimCall provisions numbers for your account specifically — the provisioning relationship that enables Full attestation is the same relationship that prevents your numbers from being shared with other tenants.

What the prospect actually sees

The prospect's screen shows: caller ID (the number and any associated name), and potentially a label applied by their carrier or analytics app.

STIR/SHAKEN attestation level influences the label risk but is not directly visible to the prospect. A prospect whose carrier analytics scored the call favorably sees a clean caller ID with no warning label. A prospect whose carrier scored it as potential spam sees "Spam Likely" or a similar label regardless of attestation level.

Attestation reduces the probability of the negative label. It does not eliminate it.

How STIR/SHAKEN interacts with per-minute vs. flat-rate carrier choice

STIR/SHAKEN implementation requires the originating carrier to hold certificates from a Certification Authority (CA) authorized by the ATIS Certificate Management Service. Carriers must maintain this certification to sign calls. Not all SIP carriers have implemented STIR/SHAKEN — particularly smaller or international-focused carriers that route primarily through VoIP trunks rather than direct PSTN interconnects.

When evaluating a SIP carrier for US/CA outbound, confirm explicitly that they provide Full (A) attestation for numbers provisioned to your account. A carrier that provides Partial (B) or Gateway (C) attestation — or no attestation at all — is structurally less favorable for high-volume US/CA outbound campaigns than one that provides Full attestation.

This is a feature question to ask before signing. UnlimCall provides STIR/SHAKEN Full attestation on US/CA outbound calls placed through numbers provisioned for your account.

Practical checklist for B2B outbound teams

Before launching a US/CA outbound campaign, verify the following at the carrier layer:

1. STIR/SHAKEN attestation level — confirm Full (A) attestation for numbers provisioned to your account
2. Number provisioning model — confirm numbers are provisioned to your account, not drawn from a shared pool
3. Number history — new numbers provisioned to your account have no prior flag history; numbers ported from high-volume shared pools may carry inherited reputation
4. Call volume ramp — starting a new number with very high volume immediately can attract analytics-provider flags; some teams ramp volume gradually over the first week with a new number
5. Analytics provider monitoring — services like YouMail and First Orion operate independent of STIR/SHAKEN; monitor whether your provisioned numbers appear in their databases

Items 4 and 5 are operational practices, not carrier guarantees. No carrier can guarantee spam-flag status with downstream analytics providers.