STIR/SHAKEN Attestation — Why It Matters for Answer Rates

What STIR/SHAKEN Is and Why Carriers Built It

STIR (Secure Telephone Identity Revisited) and SHAKEN (Signature-based Handling of Asserted information using toKENs) are complementary standards mandated by the FCC under the TRACED Act. Every US and Canadian originating carrier is required to sign calls in the SIP header using a certificate issued by the Secure Telephone Identity Policy Administrator (STI-PA). Terminating carriers read that signature and assign a trust score to the call.

The framework does three things:

• Verifies the identity of the originating carrier
• Verifies that the originating carrier has authority over the number being used as caller ID
• Provides a cryptographic chain of custody that travels with the call through the PSTN

Carriers that cannot or do not sign calls are required to include a "no signature" marker. Many downstream carriers treat unsigned calls the same as C-level calls — with maximum suspicion.

The Three Attestation Levels

A-level attestation is only achievable when three conditions are met simultaneously: the originating carrier holds a valid STI-PA certificate, the number on the call is directly assigned to an account at that carrier, and the carrier has verified the relationship between the account holder and that number.

This is why provisioning method matters. A number rented from a reseller who signs calls on your behalf cannot achieve A-level attestation — the carrier signing the call does not have a direct account relationship to the number. The signature is technically valid, but the attestation level drops to B or C.

How Attestation Level Affects Answer Rates

US mobile carriers including T-Mobile, AT&T, and Verizon have deployed call analytics at scale. Their network-level labels ("Spam Risk", "Scam Likely", "Verified") are built on a composite signal that includes STIR/SHAKEN level as a primary input.

Estimated impact by level on cold outbound calling (illustrative benchmarks, not a guarantee — actual results vary by industry, number age, call pattern, and carrier):

These are directional estimates derived from published carrier studies and industry benchmarks. Your numbers will depend on your vertical, your call patterns, and the reputation history of your numbers.

UnlimCall's Position on STIR/SHAKEN

UnlimCall supports STIR/SHAKEN signing on US and Canadian outbound calls. We target A-level attestation on eligible calls — that is, calls originating from numbers directly provisioned to your account through our carrier relationships.

What "eligible" means in practice:

• Numbers provisioned during onboarding through UnlimCall's direct carrier agreements are the highest-trust path to A-level signing
• If you bring your own numbers or route through a third-party carrier, attestation level depends on that carrier's relationship to the number
• International calls (outside US/CA) are not covered by STIR/SHAKEN — attestation frameworks in other markets (e.g., CNAP in France, Caller ID regulations in the UK) work differently

This is not a legal compliance guarantee. STIR/SHAKEN is a technical attestation framework, not a regulatory safe harbor. Whether your outbound calling program complies with applicable law — including the TCPA, TSR, and any state-level requirements — depends on factors outside the attestation framework. Consult legal counsel for compliance obligations.

Local Caller ID and Attestation Work Together

A-level attestation without a local number still displays an out-of-area code. A local number without A-level attestation gets flagged before it rings. The combination — local number, native provisioning, full attestation — is what drives the top of the answer-rate range.

This is the argument for a flat-rate outbound network with native provisioning across markets rather than buying SIP minutes from a wholesale carrier and bolting on a number reseller:

UnlimCall's model: one flat daily rate per agent seat covers unlimited outbound minutes in your licensed markets. The underlying SIP infrastructure runs through direct carrier paths — not wholesale aggregators — which is what enables the native provisioning path to A-level attestation.

What Happens Outside US and CA

STIR/SHAKEN is a North American framework. Calls to Germany, the UK, Australia, Brazil, and the other 30+ markets in the UnlimCall network are governed by different regulatory frameworks. In most markets, the relevant trust signal is Caller ID authenticity — whether the number presented as caller ID is a number you actually hold a license to use.

UnlimCall provisions local numbers in all 33 live markets through direct carrier agreements. That means you are presenting a number you are authorized to use, which satisfies Caller ID requirements in most markets. Regulatory frameworks vary; this is not legal advice.