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xAI voice agents answer calls over SIP. Its Direct SIP option lets you attach a phone number you already own, so you can put a Grok agent on a Vobiz number in any region Vobiz serves - including India, where xAI does not provision numbers itself.

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What you’ll build

An inbound calling setup where someone dials your Vobiz number, Vobiz routes the call over TLS to xAI’s SIP endpoint, and the Grok agent handles the conversation.

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Architecture

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Prerequisites

  • xAI account with a voice agent → xAI console
  • Vobiz account → Vobiz Console
  • A Vobiz phone number you want the agent to answer on

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Step 1: Add the number in xAI

In the xAI console, open your agent and add a new phone number. Select the Direct SIP tab rather than Twilio.
xAI New phone number dialog with the Direct SIP tab selected, showing the SIP URI and allowed addresses fields
Fill in the fields: The SIP URI field shows {number} as a template. xAI resolves it to the number you entered, so the address Vobiz sends to becomes +91XXXXXXXXXX@sip.voice.x.ai.
Keep transport=tls in the SIP URI. The origination URI you create in Step 2 must use the same transport, or the call will not connect.

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Allowed addresses

Allowed addresses controls which hosts xAI accepts SIP traffic from. Add the Vobiz SIP signaling IPs so calls from your trunk are accepted:
These are the India signaling IPs. For the full list including RTP media ranges, and for other regions, see IP Whitelisting.

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Step 2: Create the origination URI in Vobiz

An origination URI is the SIP destination Vobiz routes inbound calls to. Navigate to Origination URIs and create one pointing at xAI.
Vobiz Create Origination URI dialog with the xAI SIP address and TLS transport selected
Use the same number here that you entered in xAI. The URI is what xAI matches the incoming call against.

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Step 3: Create the inbound trunk

Navigate to Inbound Trunks and create a trunk that uses the origination URI from Step 2.
Vobiz Create Inbound Trunk dialog with a trunk name and the xAI origination URI selected as the primary URI
Two optional sections are available on the same screen:
  • Recording & transcription - turn on call recording for this trunk, then optionally add a recording webhook, AI transcription, and PII redaction. Each depends on the one above it.
  • Webhook configuration - set a URL to receive real-time call events over HTTP. See Callbacks for the event payloads.
Open the trunk you just created and link your Vobiz number to it under Linked Numbers.
Vobiz inbound trunk detail showing the primary URI configuration and a linked phone number
Click Link Numbers, select your number, and confirm. The trunk detail view then shows the number under Linked Numbers (1), and the trunk status reads Enabled. At this point the route is complete: the number is linked to the trunk, the trunk points at the origination URI, and the origination URI points at xAI.

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Step 5: Test the integration

Call your Vobiz number from any phone. The Grok agent should answer and begin the conversation.

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Troubleshooting

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The call rings but the agent never answers

Check that the number in the Vobiz origination URI exactly matches the number configured in xAI, including the + and country code.

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The call fails immediately

Confirm the transport is TLS in both places - transport=tls in the xAI SIP URI and TLS on the Vobiz origination URI.

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Calls are rejected by xAI

Verify the Vobiz SIP signaling IPs are present in the Allowed addresses list on the xAI number. See IP Whitelisting for the current list.

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The number is not reachable at all

Open the trunk and confirm Status is Enabled and the number appears under Linked Numbers.

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Next steps

IP Whitelisting

Full SIP signaling and RTP media IP ranges

Callbacks

Receive call events on your own endpoint

Call Recording

Record, retrieve, and download calls on this trunk

SIP Trunking

How Vobiz trunks route calls