> ## Documentation Index
> Fetch the complete documentation index at: https://docs.threetone.in/llms.txt
> Use this file to discover all available pages before exploring further.

# Register a Twilio call

> Understand the current register-call response and prepare a future call handoff without configuring an unavailable webhook.

Call registration would connect an existing provider call to the intended agent session. It is different from importing a number or initiating a new outbound call.

<Warning>
  The current [Register Twilio call](/api-reference/agents-platform/register-twilio-call) handler returns HTTP 501. It does not generate usable TwiML or start media execution. Do not configure it as a live Twilio number's voice webhook.
</Warning>

## Prepare the handoff

Identify the number owner, call direction, target workspace and agent, and the existing route that should remain active. Keep a record of the provider-side call identifier without including credentials.

<Steps>
  <Step title="Review the future request boundary">The declared request includes agent, caller, destination, direction, and optional conversation initiation data. Validate these against the selected workspace and version rather than trusting caller-supplied values.</Step>
  <Step title="Separate the two HTTP contracts">Twilio's webhook contract and the Threetone registration request are not interchangeable merely because both concern a call. A released integration must document request authentication, field mapping, and the exact response.</Step>
  <Step title="Specify failure behavior">Decide what the caller hears if registration fails, how the existing route is preserved, and who owns termination. Avoid retrying a non-idempotent registration without checking whether a session was created.</Step>
  <Step title="Require release evidence">Before changing carrier configuration, require a supported handler, documented webhook credential handoff, usable call instructions, and a successful authorized test of answer, audio, and hangup.</Step>
</Steps>

Twilio uses [TwiML instructions](https://www.twilio.com/docs/voice/twiml) to control Programmable Voice calls. A declared HTML response type in an API schema is not evidence that a working instruction document will be returned.

## Failure handling

Treat the current 501 response as an implementation boundary. Rotating credentials or retrying it cannot enable the handler. Route support questions with the operation name and response status, keeping secrets and full caller details out of the report.

## Frequently asked questions

<AccordionGroup>
  <Accordion title="Does number import enable registration?" id="twilio-register-faq-import">No. Import saves a phone record. Registration remains unimplemented.</Accordion>
  <Accordion title="Can I use registration to place a new outbound call?" id="twilio-register-faq-outbound">No. Outbound initiation is a separate operation with its own provider and runtime gates. See [Twilio native integration](/agents-platform/deploy/telephony/twilio/native-integration).</Accordion>
</AccordionGroup>


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