Twilio AI gets shortlisted for voice AI projects alongside PolyAI and HappyRobot. But the comparison only works once you see one key difference: Twilio helps build a voice agent, while the other two are bought as working agents.
Twilio handles the phone call and the conversion between the caller's speech and your agent's text. But you’re responsible for building the LLM and all of the agent's logic, which is where you could use PolyAI and HappyRobot.
PolyAI resolves inbound customer service calls. HappyRobot deploys AI workers for operational calls that deliver completed work within your business systems, and AI voice agents go live in weeks.
This guide compares all three and prices what you spend building on Twilio against what you spend buying a managed agent.
| Criteria | HappyRobot | Twilio (ConversationRelay) | PolyAI |
|---|---|---|---|
| Model | Buy: managed AI workers | Build: voice infrastructure | Buy: managed CX agent |
| Best for | Enterprise operational phone workflows | Engineering teams building a custom agent | Enterprise customer service at contact center scale |
| What you get | Deployed AI workers that complete work in your systems | Call handling, speech-to-text, and text-to-speech over a WebSocket; you bring the LLM | A managed voice agent built on its own Raven LLM and Owl ASR |
| Engineering effort | Low; Forward Deployed Engineers build with your team | High: you build and maintain the agent | Low to medium; PolyAI's team builds in about six weeks |
| Call focus | Outbound and inbound operational calls, such as collections and scheduling | Whatever you build | Inbound customer service resolution |
| Telephony | Bring your own: Twilio, Telnyx, SIP | Native (Programmable Voice) | SIP and PSTN into existing contact center stacks |
| Pricing | Quote, scoped to the deployment | Usage-based: about $0.014/min for voice, about $0.07/min for ConversationRelay, plus your LLM costs | Custom enterprise quote, per-minute model |
| Best-fit buyer | Operations and phone-heavy enterprises | Teams with engineers and the time to build | Large CX and contact center teams |
Quick Verdict: Build on Twilio or Buy a Managed Agent?
Build on Twilio if you have an engineering team but no off-the-shelf agent that fits the calls you need automated.
Twilio gives you three components:
- The phone line your callers dial
- Conversion of the caller's speech into text
- Your agent's text back into speech, and the freedom to connect any LLM you choose
If you need anything beyond these functions, such as the agent's logic and its connections into your systems, then you’re responsible for creating and maintaining it.
Buy a managed agent if you want calls handled without having to build the system to handle them. PolyAI is useful for inbound customer service at contact center scale. Choose HappyRobot for operational calls where the AI worker completes follow-up within systems like Salesforce and McLeod. The deployment with HappyRobot runs in weeks with Forward Deployed Engineers.
Build vs Buy: The Real Decision
Every decision on the voice AI platform comes down to one question: who builds and maintains the agent. This will also help you decide what to spend and when to launch, because it determines who fixes the system when a call goes wrong.
What building on Twilio actually involves
Twilio's Conversation Relay handles the phone call and converts the caller's speech into text. It also converts your agent's replies back into speech.
Everything between those two conversions is yours to build, and Twilio's does not integrate directly with any LLM provider.
Building on it, your engineers will need to:
- Host a WebSocket server that receives the caller's words as text
- Connect the LLM and pay its usage separately from the Twilio bill
- Write the conversation logic, including every escalation path
- Tune the latency until replies land inside a natural pause, because a slow reply reads as a dropped line to the caller
- Build every connection into your own systems, from the CRM to the scheduler
A CMO reviewing Twilio on G2 calls it a bring your own engineer platform.
What buying a managed agent involves
A managed platform hands you a finished agent where the vendor maintains it after the launch. That way, your team works with a running system instead of a codebase.
PolyAI will have their team design a customer service agent and launch it. Changes after launch go through PolyAI's team, which suits a CX organization that wants the agent managed end-to-end.
With HappyRobot, buying looks like this:
- Forward Deployed Engineers build the first workflows with your team, in your offices
- The first workflows reach production in weeks
- Your phone numbers stay where they are, since HappyRobot runs on the Twilio, Telnyx, or SIP lines you already have
- HappyRobot maintains the models and the voice stack after launch so that the updates never require your engineers to work on it
- Every workflow is visible in a node-based builder, so your operations team can read what the agent does at each step
The choice boils down to what you want: better control or faster speed. Building on Twilio means choosing every component yourself. Buying an AI voice agent means accepting the vendor's stack and getting months of engineering time back.
What is Twilio AI Conversation Relay?
Twilio AI is the collective name for the voice AI building blocks on Twilio's communications platform. Conversation Relay is the specific developer tool for building voice agents that connects speech-to-text and text-to-speech with the LLM of your choice over a WebSocket API.
With Twilio, you’re essentially getting the platform behind the phone calls and text messages of hundreds of thousands of businesses. It's also the reason why Gartner named it a Leader in the 2026 Magic Quadrant for CPaaS for the fourth consecutive year.
How Conversation Relay works
Conversation Relay dispatches each conversation turn between the live phone call and a server you host, in four steps:
- The caller speaks, and Twilio converts that speech to text through providers such as Google Speech-to-Text.
- Twilio streams the text over a WebSocket to your server.
- Your server sends the text to whichever LLM you run and receives the reply.
- The reply streams back to Twilio, where text-to-speech providers such as Amazon Polly read it to the caller.
Twilio manages the call itself, including when the caller interrupts mid-sentence. On your end, you’ll have to provide the server and the LLM along with every integration into your own systems.
Cost: Conversation Relay costs about $0.07 per minute on top of voice calling at about $0.014 per minute, and your LLM usage bills separately from your AI provider.
Where Twilio is the right choice
Twilio fits engineering teams whose agent does not exist as a product they can buy, whether that means a unique workflow or a proprietary model at the core. The reputation among developers holds up in reviews, where G2 reviewers rate the documentation as the gold standard.
The infrastructure carries calls in over 180 countries, so an agent built on it can reach your customers wherever they are. The trade-off remains a challenge since Twilio hands you working infrastructure, but the agent itself remains your engineering project from the first prompt to every update after launch.
PolyAI: The Managed Agent for Customer Service Calls
PolyAI offers a finished voice agent for inbound customer service, built and launched by its own team. Their product’s core goal is to make an AI voice agent sound and respond like a person on a customer service line.
What you get with PolyAI
- Its own models: Raven, an LLM trained on over one billion enterprise customer conversations. And Owl, the speech recognition model tuned on real phone audio, complete with background noise, because that is what callers actually sound like.
- A vendor-run build. PolyAI's team designs the agent and launches it in about six weeks, and changes after launch go through PolyAI's team.
- Documented returns. A Forrester study commissioned by PolyAI reports a 391% return on investment over three years, with average savings of $10.3 million per customer.
There is a limit to where PolyAI fits. A five-star Gartner reviewer calls the total cost premium and harder to justify for smaller, low-volume operational workflows.
HappyRobot: The Managed Agent for Operational Calls
HappyRobot deploys AI workers that make and answer business phone calls, then complete the follow-up work inside systems like Salesforce, McLeod, and Gmail.
A collections call ends with the payment commitment logged in the receivables system. Similarly, a carrier scheduling call ends with the appointment booked and the record updated.
This is the difference between an AI phone agent that resolves conversations and an AI worker that finishes the work each conversation creates. HappyRobot puts both to work, while PolyAI stops at the phone agent and Twilio only gives you the parts to build an agent yourself.
What you get with HappyRobot
- Workflows that combine AI judgment with fixed business rules. The agent makes judgment calls where the conversation needs them. Also, it follows the rule where it does not, which is how a payment negotiation stays flexible while the compliance script stays exact.
- Deployment led by Forward Deployed Engineers. You get first workflows built alongside your team, so voice automation is working when it reaches you.
- Bring-your-own telephony. A company already running Twilio numbers keeps them, with HappyRobot's AI workers handling the calls on top.
Proof from deployments
- Kuehne+Nagel handles 78% of connected calls end-to-end across its Air Logistics operations, which raised team capacity by 47%.
- Naturgy evaluated close to 30 vendors and took HappyRobot from POC kickoff to production in 3 months, scoring 9.4 out of 10 in customer satisfaction within the first weeks.
- 8 of the top 10 freight brokerages run on the platform today.
Book a HappyRobot demo to scope your first workflow.
Head-to-Head: Where Each Platform Wins
We've compared the three platforms in two pairings. HappyRobot vs Twilio is a build-or-buy question, while HappyRobot vs PolyAI comes down to which calls your business runs.
HappyRobot vs Twilio: buy a working agent or build your own
There is no feature-to-feature comparison here because Twilio is the infrastructure on which an agent is built, and HappyRobot is the finished agent. The honest way to compare them is to look at what your team does in the first 90 days.
On Twilio, those 90 days are engineering time. Which means your team will host the server, connect the LLM, and test conversation logic before the agent can take a production call.
With HappyRobot, the same 90 days are operating time, during which the first workflows go live within weeks, and your team then reviews call outcomes and expands what the AI workers automate.
You can also run both at once. Twilio provides the phone line, HappyRobot provides the agent talking on it. A company on Twilio can keep its numbers, and the build-versus-buy decision applies only to the agent.
HappyRobot vs PolyAI: operational calls or customer service calls
The two differences between HappyRobot and PolyAI are call direction and the channels surrounding the call.
- On call direction: PolyAI answers the phone, whereas case studies are built on inbound customer service lines. HappyRobot also dials out, which is how collections lists get worked and how a carrier gets called before a pickup window closes.
- On the channels around the call: HappyRobot's AI workers handle the email and SMS threads connected to their phone calls, with DHL running hundreds of thousands of emails and millions of voice minutes through them annually. PolyAI is voice-first by design. The full HappyRobot vs PolyAI comparison covers this pairing in depth.
Pricing Compared (2026)
There are no publicly available sources that provide the full pricing for a working agent. But some costs apply to different functions each of these tools does.
- Twilio bills usage at about $0.014 per minute for the call and $0.07 per minute for ConversationRelay, plus your LLM provider's charges. The higher cost occurs outside the invoice when you hire engineers to build and maintain the agent. Their support plans alone range from $250 to $5,000 per month, depending on the tier.
- PolyAI: Get quotes for custom enterprise contracts on a per-minute model, with pricing varying based on many factors such as call volume and the complexity of the workflows the agent handles.
- HappyRobot: Pricing depends on the scope of the deployment rather than on a per-minute basis, so the number reflects the workflows being automated.
Book a demo for a scoped quote.
How to Choose: Build or Buy
Four questions settle this decision faster than any demo.
- Do you have engineers to spare for six months or more?
Building on Twilio consumes real engineering capacity at launch and for every update after. If your team does not have that capacity, then building it could prove costly. - Does a finished agent already fit your calls?
Customer service queues fit PolyAI. Collections, scheduling, and outbound sales are a good fit for HappyRobot. Build your own only when the workflow you need isn't offered as an existing product by any vendor. - Do your calls end with work in other systems?
If every call creates a task in Salesforce, McLeod, or your ticketing system, the agent needs write access to those systems on day one. HappyRobot includes that integration work in the deployment. On Twilio, your engineers build it. - How soon does this need to be live?
It takes weeks for managed platforms to be up and running. Twilio goes live whenever your engineering team finishes the build. A Trustpilot reviewer mentions taking one week just for the registrations.
Final Verdict
The Twilio AI decision is a build-vs-buy call before it is a vendor call. Twilio wins for teams that have the engineers and want to build a fully custom agent. PolyAI works best for enterprise customer service at contact center scale.
HappyRobot is the top pick for operational voice. You get a deployed agent that completes real work in systems like Salesforce and McLeod, goes live in weeks, and skips the need to build on raw infrastructure.
Book a HappyRobot demo to scope your first workflow.
