Pick an AI voice agent by starting with your calls, not the technology. List the call types you want it to handle, the systems it needs to read or update, and the point where a person takes over. Then compare options on compliance, language support, interruption handling and who owns the finished build. That order works whether you’re shopping for an AI phone answering service or building something custom.
What does an AI voice agent actually do on a call?
It listens, works out what the caller wants, and answers out loud. Twilio’s ConversationRelay documentation describes one common way to do this. The platform handles speech-to-text, text-to-speech, session management and low-latency audio. Your own application receives the caller’s words as transcribed text over a WebSocket and sends its replies back as text, which the platform turns into speech.
OpenAI’s Realtime API takes a different route. It’s a speech-to-speech approach where the model works directly with audio, keeps track of the conversation and can call tools. OpenAI recommends it when a call should feel immediate, with callers able to interrupt and natural turn-taking. It also points to a separate guide that compares this design with chained pipelines, where speech and text steps run one after another.
An AI receptionist is usually this same technology given a front-desk job: answer, qualify, book, route or take a message. The AI is only part of it. Tools, handoffs and guardrails, which OpenAI says you attach to the agent, are what make it useful.
Is an AI voice agent worth adopting for your business?
The honest answer comes from your own call log, not a vendor demo. Pull a few weeks of calls and sort them by reason. If a large share are routine, such as hours, appointment changes or order status, an agent has plenty to work with. If most calls are tangled, emotional or high-stakes, you’ll want it to do less.
Typical ConversationRelay call
- Caller speaks
- Speech becomes text (STT)
- Your app receives the text over a WebSocket
- Your app sends back a text reply
- Reply becomes speech (TTS)
- Caller hears the answer
Source: Twilio
Here’s an imagined example. A small HVAC company finds that many of its after-hours calls are people asking to book a visit or check an appointment. That’s a good candidate. A call about a flooded basement should go straight to a technician’s phone.
- Count calls by reason and by time of day, including missed ones.
- Mark which call types follow a fixed script and which need judgment.
- List the systems the agent would need to reach, such as a calendar, CRM or order system.
- Decide what a bad call costs you, then set rules for when the agent must hand off.
What drives the cost and effort of an AI phone answering service?
Pricing is the first thing to pin down, and the documentation pages these examples draw on don’t quote any prices. Ask every vendor how usage is billed and what’s included in setup.
Beyond price, effort mostly comes from five places.
Integrations come first. Every system the agent touches is a tool to build, test and secure. Languages are next. In ConversationRelay you add one language configuration for each language a session may use, and automatic language detection only works with Deepgram for speech-to-text and ElevenLabs for text-to-speech. Other providers in that mode end the session with an error.
Compliance is the third driver. Twilio says you can run card-data voice workflows through ConversationRelay that meet PCI rules, provided the speech-to-text and text-to-speech providers you choose are PCI compliant. It warns that not every provider is. It also says you shouldn’t put card data in fields such as welcomeGreeting, hints, custom parameters or handoffData. For healthcare, it calls the service HIPAA Eligible when configured properly, and you need a signed Business Associate Agreement with Twilio.
Call behavior is the fourth. ConversationRelay has a setting that controls whether a caller’s speech or keypad input stops the agent mid-sentence. Getting that feel right takes testing with real callers.
Upkeep is the fifth. OpenAI tells teams still on its beta Realtime interface to move to the GA version, with changed headers, endpoints and event names. Platforms change, so budget for maintenance.
Which type of option fits your business?
Twilio ConversationRelay, the OpenAI Realtime API and Google Cloud CCAI Platform are three different kinds of product. None of them is a finished answering service you sign up for and forget. Treat them as examples of the layers you’ll meet when you talk to vendors.
What should you ask a vendor or partner?
Whether you’re evaluating a hosted AI phone answering service or a custom build, the questions are similar. Ask for answers in writing, and ask to hear sample calls on your own scripts.
A development partner such as Aranv, which builds AI voice agents, would typically start from the call audit described above. It would then map the agent’s tools to your systems, define handoff rules, and test with realistic calls before going live. Whoever you pick should be able to explain each of those steps plainly.
- Which speech-to-text, text-to-speech and AI model providers sit behind the service, and can they be swapped?
- How does the agent hand a caller to a person, and what context does the person get?
- What happens when a caller interrupts, goes silent or speaks another language?
- Which of your regulations apply (PCI, HIPAA or others), and what agreements will you sign?
- How is usage billed, and what costs extra for setup, changes or extra languages?
- Who owns the scripts, integrations and call data if you leave?
- What reporting will you get on call outcomes and caller satisfaction?
| Option | Best for | Watch out for |
|---|---|---|
| Twilio ConversationRelay | Teams with their own AI application. The platform handles speech-to-text, text-to-speech and call sessions. | Provider choices affect PCI status and language detection. Onboarding and an AI addendum come first. |
| OpenAI Realtime API | Conversational, immediate calls with interruptions, natural turn-taking and live tool use | You build the application around it, and older beta integrations need migrating to the GA interface |
| Google Cloud CCAI Platform | Organizations that want a contact center platform with routing, virtual agents and handoff to human agents | It’s a full platform, so check country and region availability and how it fits your CRM |
What should you do next?
This week, pull your last month of calls and sort them by reason, time of day and outcome. Pick the two or three call types that are repetitive and low-risk, write down the systems each one needs, and bring that list to your first vendor conversation. It’ll make every demo more honest and every quote easier to compare. Want help with this? See our work on AI voice agent development and AI agent development, or book a meeting with our team.
Frequently asked questions
Is an AI receptionist the same as an AI voice agent?
Usually, yes. An AI receptionist is a voice agent set up for front-desk work like answering, booking and routing calls. Ask any vendor what it can actually do, not just what it’s called.
Can an AI voice agent handle card payments or healthcare calls?
Twilio says ConversationRelay can support card-data voice workflows that meet PCI rules, as long as the speech providers you pick are PCI compliant. It also calls the service HIPAA Eligible when configured properly, with a signed Business Associate Agreement. Your setup still has to meet those conditions, so confirm the details with your vendor and your own compliance adviser.
Should I buy an answering service or build a custom voice agent?
A hosted service is faster to start when your calls are simple and standard. A custom build makes more sense when the agent has to work with your own systems or follow specific rules. Compare both against your call audit and ask about ownership and switching costs.
Related reading
Sources
- ConversationRelay, Twilio
- Realtime API, OpenAI
- Contact Center AI Platform documentation, Google Cloud
Researched from the sources above with AI assistance, then checked against them before publishing.
