By Sagar Shankaran, Founder of CallSphere
What attestation level your AI calls actually receive, why Level A is the only one that lights up Caller Verified on the receiver's screen, and how to get there with a Twilio-style trust profile.
Key takeaways
An AI outbound call signed at Level A reads "Caller Verified" on supported handsets. The same call signed at Level C reads as a possible spam call on most carriers. The difference is whether your originating provider can vouch for both you and the number on the From header.
flowchart TD
Out[Outbound campaign] --> Twilio[Twilio Voice API]
Twilio --> STIR[STIR/SHAKEN attestation]
STIR --> Carrier[Originating carrier]
Carrier --> Term[Terminating carrier]
Term --> Recipient[Recipient phone]
Recipient --> Webhook[/voice webhook/]
Webhook --> Agent[AI sales agent]STIR/SHAKEN is a pair of standards (STIR for the cryptographic identity passport, SHAKEN for the carrier framework) that the FCC mandated for IP-based originations starting June 30, 2021, with extension deadlines closed for nearly all carriers by mid-2025. Each call carries a SIP Identity header signed by the originating provider, asserting one of three attestation levels: A (Full) when the provider knows the customer and verifies the right to use the From number, B (Partial) when the provider knows the customer but cannot verify the number, and C (Gateway) when the provider only sees the call entering its network from elsewhere. The FCC's December 2025 update tightened reporting; carriers now file attestation statistics quarterly and small-carrier exemptions have largely been eliminated.
For AI outbound, attestation level is essentially answer-rate. CTIA-aligned analytics partners (TransUnion, First Orion, Hiya) take attestation as a major signal in spam scoring. Calls signed C trend toward "Spam Likely" labels in days; calls signed A retain neutral or positive labels.
To earn Level A on your AI outbound, your originating carrier must (1) have a verified business identity for you and (2) confirm that the From number you assert is a number you control. The cleanest path is buying numbers from the same carrier you originate with and registering them inside that carrier's trust product. Bring-your-own numbers ported in get there too, but the carrier needs ownership records.
Hear it before you finish reading
Talk to a live CallSphere AI voice agent in your browser — 60 seconds, no signup.
For AI in particular, FCC has clarified that AI-generated voices are "artificial" under the TCPA. STIR/SHAKEN does not exempt you from TCPA consent. A call can be Level A signed and still illegal if you lack consent. Attestation is about who you are, not whether the call should happen.
Every CallSphere outbound call rides Twilio Programmable Voice with a Customer Profile in Twilio Trust Hub plus a SHAKEN/STIR Trust Product attached. Numbers we provision through Twilio are bound to that profile, so calls sign Level A by default. Sales Calling AI runs five concurrent outbound calls per tenant on Twilio with TCPA opt-out flows recorded inline. After-Hours AI fires per-contact outbound calls plus SMS to on-call staff with a 120-second timeout. Healthcare AI is HIPAA and SOC 2 aligned; the same trust profile signs its outbound confirmations. Where customers want to bring their own numbers, we walk them through Twilio's hosted-number SHAKEN/STIR onboarding so attestation does not silently downgrade.
Will Level A guarantee my AI call rings through cleanly? No. It is a strong signal, not a free pass. Behavior matters too: short calls, low pickup rates, and complaint rates still drag your reputation down.
Does STIR/SHAKEN apply to international calls? STIR/SHAKEN is US-centric. Cross-border calls land at the receiving country's edge with a Level C if no peering trust exists. Canadian carriers run their own SHAKEN deployment under CRTC oversight.
Still reading? Stop comparing — try CallSphere live.
CallSphere ships complete AI voice agents per industry — 14 tools for healthcare, 10 agents for real estate, 4 specialists for salons. See how it actually handles a call before you book a demo.
Can my AI agent spoof a different From number for a callback? Only if you control or are authorized to use that number. Using a number you do not own degrades to B or C and may violate the TRACED Act regardless.
What if my originating carrier signs C on my numbers? That usually means the trust product or number assignment is misconfigured. Open a ticket; the fix is paperwork, not infrastructure.
Does Branded Calling fix bad reputation faster? It speeds up the recovery curve once your behavior is clean, but it does not paper over real complaints.
Start a 14-day trial with Level A signing on Day 1, browse pricing, or contact us for trust-product help.
Written by
Sagar Shankaran· Founder, CallSphere
Sagar Shankaran is the founder of CallSphere, where he builds production AI voice and chat agents deployed across healthcare, hospitality, real estate, and home services. He writes about agentic AI, LLM engineering, and shipping voice agents that handle real calls in production.
See how AI voice agents work for your industry. Live demo available -- no signup required.
A VoIP telephone number is a phone number that routes calls over the internet instead of copper lines. Learn what a VoIP number is, how to get one, what it costs, and how to pair it with an AI voice agent in 2026.
How we built a fault-tolerant HVAC emergency triage and tech-dispatch platform on Kubernetes — three-tier CQRS, 11 micro-agents on the OpenAI Agents SDK + LangGraph, NATS JetStream, DTMF/SMS/WebSocket acceptance, circuit breakers, and an evaluation pipeline that catches regressions before they wake a tech at 3 AM.
STIR/SHAKEN, branded calling, opt-in lists, carrier reputation. How CallSphere builds outbound trust vs Vapi defaults. Real-world spam-flag remediation.
Voicemail detection accuracy makes or breaks outbound voice AI. CallSphere VoicemailAnalyzerAgent + Twilio AMD vs Vapi defaults. Real call examples included.
DTMF tone capture during agent speech, IVR-style menus, key suppression. How CallSphere handles DTMF via Twilio + custom logic vs Vapi defaults.
When Twilio Conversational Intelligence and ConversationRelay are enough, when to roll your own, and the operating-cost math behind the decision in 2026.
© 2026 CallSphere LLC. All rights reserved.