AI voice agents that answer the phone and book the appointment

The latency budget for one turn

People leave very short gaps between turns. A cross-language study in PNAS (Stivers et al., 2009) found the most common gap in all ten languages it studied was between 0 and 200 milliseconds. No AI pipeline matches that, but every stage adds delay, so we budget each one and measure it on real calls.

Interruptions matter as much as speed. When a caller talks over the agent, it should stop within a moment and listen, not finish its sentence.

Hosted platform or self-built?

Hosted wins for a first launch and modest volumes. Self-built wins when volume is high enough that per-minute platform fees hurt, when you need a language or provider a platform does not support, or when data must stay in a specific country.

Telephony in the US and India

In the US we use Twilio or a carrier SIP trunk, and either port the practice’s number or forward to the agent so callers keep dialling the number they know. Twilio signs a BAA for its HIPAA-eligible products, which cover US voice traffic.

India is different. Calls run through licensed cloud-telephony providers or operator SIP trunks, and outbound calling is shaped by TRAI’s commercial-communication regulations (TCCCPR), amended in February 2025. Promotional calls must come from 140-series numbers, by businesses registered with their telecom operator under that framework, and callers can block them through the do-not-disturb registry. Entities regulated by RBI, SEBI, IRDAI or PFRDA, and government bodies, must use 1600-series numbers for service and transactional calls to existing customers and citizens. Confirm the current rules with your telephony provider before any outbound campaign.

A HIPAA checklist: the BAA chain

A voice call carries protected health information through more vendors than people expect. Every one of these needs a BAA, or must never see PHI:

• Telephony carrier and number provider
• Voice platform, if hosted
• Speech-to-text provider
• Language model provider
• Text-to-speech provider, which receives the names and appointment details it speaks
• Cloud host, database and backups. HHS guidance says a provider is still a business associate even if it stores only encrypted data without the key
• Logging, tracing and analytics tools that store transcripts
• Recording storage, plus any integration middleware between the agent and the EHR

Beyond the paperwork: retention limits for recordings and transcripts, role-based access, audit logs, and a recording notice where state law requires every party to consent. Our HIPAA readiness work covers the rest of the programme; we help you prepare, we do not certify.

Designing the human handoff

• Triggers: the caller asks for a person, the agent misunderstands twice, the call is clinical or urgent, or the caller is upset.
• Emergencies: the agent tells the caller to hang up and dial 911 (or 112 in India) and flags the call. It never tries to triage.
• Warm transfer: staff hear or see a short summary before they pick up, so the caller does not repeat themselves.
• Nobody free: the agent takes a callback request with a summary and gives an honest callback window. It never loops.

Outbound calls and consent in the US

On 8 February 2024 the FCC ruled that AI-generated voices count as “artificial” under the TCPA. Informational calls such as reminders generally need the person’s prior express consent, and telemarketing calls need prior express written consent. Since 11 April 2025, people can revoke consent by any reasonable means, and requests must be honoured within 10 business days. State laws add calling hours and their own consent rules. We build the consent store and opt-out handling (including “stop calling me” said mid-call); your counsel signs off the campaign.

Testing with simulated callers

Before go-live we run hundreds of simulated calls: elderly callers, noisy streets, strong accents, people who interrupt, change their minds, give a wrong date of birth or try to get details about another patient. Each call is scored against the expected outcome. The suite reruns on every change, and live monitoring tracks transfer rate, booking completion and response latency.

What drives the cost

• Minutes: call volume × call length, multiplied across platform, model, speech and telephony charges.
• Model and voice choice: larger models and premium voices cost more per minute.
• Telephony: numbers, carrier minutes and, for outbound in India, registration.
• Integrations: EHR and practice-system work is often the largest build cost.
• Compliance: BAA add-ons, recording storage and reviews.

Indian languages: what to expect

Speech recognition and synthesis for Hindi, Tamil, Malayalam, Telugu and other Indian languages have improved quickly, with providers such as Sarvam and open models from AI4Bharat focusing on them. Code-mixed speech, names, addresses and numbers over narrowband phone audio are still hard. Start with one language, let callers choose at the start, confirm key details by SMS or WhatsApp, test with real speakers of the local dialect, and keep a human fallback.

How to choose a voice agent partner

• Can they show per-stage latency from a live system?
• Will they list every vendor that hears your callers and its BAA or DPA status?
• Do they test with simulated callers before your patients hear it?
• Is the handoff designed, or just “transfer to reception”?
• Will they say when a hosted platform is cheaper than a custom build?