STIR/SHAKEN Attestation: What VoIP Resellers Need to Know in 2026

For most of telecom’s history, a phone number was effectively a self-attested identity. The dialing system trusted whatever caller ID the originating carrier handed it. The result, by the late 2010s, was a robocall problem so severe that consumers had stopped answering calls from numbers they didn’t recognize — costing legitimate businesses billions in missed customer interactions.

STIR/SHAKEN is the regulatory and technical answer to that problem. It’s now four years into mandatory enforcement on the major US carriers, and the practical effects on call delivery are well-understood enough to plan around. This guide covers what the three attestation levels mean, what determines yours, and what resellers can do to maximize legitimate-call delivery in 2026.

The Three Attestation Levels

STIR/SHAKEN is built around the originating carrier signing each outbound call with one of three attestation levels:

A-attestation (Full Attestation). The originating carrier verifies that the calling party is a known customer AND verifies that the calling party has the legal right to use the calling phone number. This is the highest trust level.

B-attestation (Partial Attestation). The originating carrier verifies the calling party as a known customer but cannot verify their right to use the specific calling number. Common for businesses calling from numbers acquired outside the carrier’s own inventory.

C-attestation (Gateway Attestation). The originating carrier can verify only that the call is entering the network through a known gateway. Cannot verify the calling party identity or number ownership. The lowest trust level.

Calls signed with A-attestation are delivered with the highest confidence. B-attestation calls usually go through but may be flagged on some terminating networks. C-attestation calls are the most likely to be labeled as “Spam Likely” or blocked outright.

Why This Matters for Resellers

If you operate a VoIP reseller business — whether under a private brand or as a managed-services partner — your customers’ calls flow through your platform’s attestation chain. The attestation rate your customers experience is structurally determined by:

1. The carrier-of-record relationship for each phone number in your customer’s inventory
2. Whether numbers were acquired through your platform vs ported in from elsewhere
3. The platform’s compliance posture with the FCC’s Robocall Mitigation Database
4. How quickly the platform updates SPID (Service Provider ID) records after porting events

A reseller serving a customer base with primarily ported-in legacy numbers will see a higher percentage of B-attestation than a reseller whose customers acquired numbers through the platform from day one. This is not a bug — it’s the system working as designed. But it has practical revenue implications.

What Determines Your Attestation Rate in Practice

Three structural factors:

Number provenance. Numbers that originated on your platform’s carrier network attest at A-level by default. Numbers ported in from a different carrier attest at B-level until the SPID record propagates and the new carrier’s relationship is fully established (typically 24-72 hours, sometimes longer for certain LATAs).

Customer onboarding hygiene. Customers who provide complete and accurate company registration data — legal entity name matching the BTN (billing telephone number) record, current physical address, contact information — attest at A-level reliably. Customers with incomplete or inconsistent records may drop to B-level even on platform-acquired numbers.

Robocall Mitigation Database registration. Carriers that haven’t filed a current Robocall Mitigation Plan with the FCC (or whose plan is incomplete) may have ALL their attestation downgraded by terminating carriers as a precaution. This is rare among established platforms but is a hard floor on attestation if it happens.

How to Maximize Legitimate Delivery

For resellers operating in 2026, the practical steps are:

Audit number provenance quarterly. Pull a report of every customer phone number with its current attestation level. Numbers attesting at B or C deserve investigation — usually it’s a stale SPID record that a quick reissue will fix.

Make complete onboarding non-optional. Don’t let customers onboard with incomplete BTN records. The 5 minutes of friction at signup saves quarters of degraded delivery later.

Verify your platform’s RMD filing. Ask your platform partner directly: when did you last file your Robocall Mitigation Plan, and is it current? A platform that hesitates on this question is a platform with delivery risk.

Monitor your numbers in third-party reputation databases. Several public reputation services let you check whether your customer numbers are flagged as spam. A flagged number can be remediated through the platform’s process — but you have to know it’s flagged first.

Set customer expectations honestly. If a customer ports in 50 legacy numbers, tell them upfront that their first 30 days of calls will see a higher spam-flag rate while the SPID records propagate. Managed expectations beat surprised escalations.

What’s Changing in 2026

Three developments worth watching:

Toll-free attestation enforcement is tightening. The FCC has been clear that toll-free numbers will receive equivalent SHAKEN treatment to geographic numbers, including attestation requirements at the originating carrier. Resellers selling toll-free should verify their platform’s attestation posture for TFNs specifically.

Cross-border attestation is gaining momentum. US-Canada call delivery has been a particular pain point. The CRTC has signaled increasing alignment with FCC SHAKEN requirements; resellers serving cross-border customers should expect tighter attestation expectations on Canada-originating calls in 2026 and 2027.

Display-name verification (RCD — Rich Call Data) is maturing. Beyond just the number, terminating carriers are beginning to honor signed display names (“Acme Plumbing — 416-555-1234”). Resellers whose platforms support RCD will get better customer outcomes than those whose platforms don’t.

Bottom Line

STIR/SHAKEN attestation is no longer a back-office compliance concern — it’s a primary determinant of call delivery rates and, by extension, customer outcomes. Resellers who treat attestation as an active operational metric (audit quarterly, onboard customers fully, verify platform compliance, monitor reputation databases) will see materially better delivery rates than those who treat it as the platform’s problem to solve.

The platforms have done most of the heavy lifting; the residual responsibility is shared with resellers. Owning the residual is a competitive advantage in 2026.