Twilio, Vapi, Sonetel — picking the voice AI stack that fits your team

For a long time, "automated phone support" meant a frustration-inducing IVR tree: "Press 1 for Sales, Press 2 to be ignored." Voice AI has changed that. You can now build a conversational agent that answers the phone, understands a messy human sentence, looks up a tracking number, and resolves the issue—all in natural language.

But while the LLM part of voice is similar to text, the "plumbing" is drastically different. In voice, 200ms of latency is the difference between a natural conversation and an awkward mess. Audio quality, global phone number availability, and PSTN (Public Switched Telephone Network) reliability are the new battlegrounds.

Beamdesk supports three primary voice stacks. Each fits a different type of team and use case.

1. Twilio: The Developer's Choice

Twilio is the industry standard for a reason. It offers the most granular control over every aspect of the call. If your team already uses Twilio for SMS or has a complex existing IVR that you need to augment with AI, this is the way to go.

With Twilio, you use TwiML (Twilio Markup Language) to orchestrate the call. Beamdesk plugs in as a <Connect><Stream> or <Gather> endpoint. This allows you to do things like: "Play this recorded greeting, then hand off to the Beamdesk AI, but if the customer says 'emergency,' drop the stream and bridge the call to our on-call mobile number."

Best for: Teams with existing Twilio infra or complex routing needs.
Pros: Full control, rock-solid PSTN reliability, global SMS integration.
Cons: Highest technical complexity to set up; latency can be higher if not optimized.

2. Vapi: The Voice-First Newcomer

Vapi is built specifically for conversational AI. They handle the messy parts of voice—noise cancellation, echo suppression, turn-taking (knowing when the customer has finished talking), and ultra-low-latency streaming—as a single platform.

Integrating Vapi with Beamdesk is the "no phone team needed" option. You point your Vapi assistant at your Beamdesk persona, and we handle the knowledge retrieval and tool calling. Because Vapi is optimized for the WebSocket handshake between the audio stream and the LLM, it often feels the most "human" in its response timing.

Best for: Startups or teams building a voice AI from scratch without legacy phone debt.
Pros: Lowest latency, excellent turn-taking logic, fastest setup.
Cons: Less granular control over traditional PSTN features; newer platform.

3. Sonetel: The Global Enterprise Play

Sonetel excels at global PSTN coverage. If you need local phone numbers in 150+ countries and need to bridge those calls into a central AI hub with consistent quality, Sonetel is the specialist.

We often see Sonetel used by B2B companies with multinational customers. They use Sonetel to provide a local presence in Europe, Asia, and the Americas, all routing back to a Beamdesk persona that can handle multilingual support using the same Knowledge Base.

Best for: Multinational B2B companies requiring global reach and PSTN stability.
Pros: Massive global number inventory, high-quality international routing.
Cons: Interface can feel dated; less "AI-native" features than Vapi.

The Routing Pattern: Voice vs. Text

In a Beamdesk voice integration, the flow follows our standard "Honest AI" principles, but with a stricter confidence bar.

voice_call_received:
  source: +44 20 7946 0958 (UK)
  persona: global_support_vapi
  
  step 1: identify customer via phone number
  step 2: listen to query ("where is my order?")
  step 3: KB lookup with citation enforcement
  step 4: if confidence > 0.90 -> synthesize reply
  step 5: if confidence < 0.90 -> bridge to human

Because you can't "edit" a voice reply in real-time, the model's confidence threshold is usually higher (e.g., 90% vs 80% for email). If the AI isn't sure, it's better to say "Let me get a human specialist on the line for you" than to stumble through a half-correct answer.

The Honest Take on Voice AI

Voice AI is hard. It's much harder than text. You have to deal with accents, background noise, people talking over the AI, and the psychological expectation of a "real" conversation.

Our advice: don't start with full replacement. Start with after-hours coverage. Use the AI to handle simple, high-volume queries (order status, FAQ) during times when your human team is offline. This allows you to gather real audio data, refine your persona's turn-taking, and build trust in the system without risking your peak-hour customer experience.

Whether you choose the control of Twilio, the speed of Vapi, or the reach of Sonetel, the goal is the same: making the phone a place where customers get answers, not just music.