Build a Voice Agent That Holds a Live Call on Telnyx Edge Compute

Getting an AI agent to answer a phone call is only the beginning.

The harder part is keeping the call going.

This example builds a voice agent on Telnyx Edge Compute that answers an inbound call, speaks a greeting, listens with streaming transcription, sends the caller's speech to Telnyx AI Inference, speaks the reply with TTS, and then goes back to listening.

Code: https://github.com/team-telnyx/telnyx-code-examples/tree/main/edge-voice-agent-holds-call

The core flow is:

call.initiated
  -> answer
call.answered
  -> speak greeting
call.speak.ended
  -> start transcription
call.transcription final
  -> stop transcription
  -> run LLM turn
  -> speak reply
call.speak.ended
  -> listen again
call.hangup
  -> persist final call state

Each live call gets a VoiceAgent

actor keyed by call_control_id

.

That actor stores:

POST /webhooks/voice

receives Call Control webhooksGET /debug/call?call_control_id=<call_id>

inspects actor statePOST /debug/respond

tests an LLM turn without a live callGET /health/liveness

and GET /health/readiness

support health checksThe VoiceAgent

extends the Agent SDK Agent

class from @telnyx/edge-runtime

.

It uses:

this.messages.add()

to store caller and assistant turnsthis.messages.toOpenAI()

to format history for the modelthis.setState()

and this.getState()

for durable call statethis.env.TELNYX.ai.openai.chat.createCompletion()

for zero-credential inference through the [telnyx]

bindingThe model call looks like this:

const completion = await this.env.TELNYX.ai.openai.chat.createCompletion({
  model,
  messages: [{ role: "system", content: SYSTEM_PROMPT }, ...history],
  max_tokens: 200,
  temperature: 0.5,
});

The webhook handler speaks the returned text through Call Control TTS.

The sample uses Call Control streaming transcription because the app owns the conversation loop.

The caller speaks. Telnyx sends a final transcript. The app stops transcription, runs the LLM turn, speaks the reply, and starts transcription again after TTS ends.

That gives you room to add your own logic:

npm install
telnyx-edge ship

Set the Call Control API key as an Edge secret:

telnyx-edge secret set TELNYX_API_KEY your_telnyx_api_key

Point your Call Control application webhook to:

https://edge-voice-agent-holds-call-<id>.telnyxcompute.com/webhooks/voice

Then call the Telnyx number assigned to that Call Control application.

Before shipping this pattern for real callers, I would add:

But even as a starter, this is a useful reference for building a voice agent that can actually stay on the call.

Resources: