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Smallest AI builds real-time voice agents. Its SIP Trunking option lets you import a phone number you already own, so you can run a Smallest AI agent on a Vobiz number anywhere Vobiz operates.

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What you’ll build

A two-way setup on a single Vobiz number:
  • Outbound - the Smallest AI agent places calls through your Vobiz outbound trunk.
  • Inbound - calls to your Vobiz number route through an inbound trunk to the Smallest AI agent.
Each direction uses its own trunk, so configure both.

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Architecture

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Prerequisites

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Part 1: Outbound calls

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Step 1: Create a SIP credential in Vobiz

Smallest AI is cloud-hosted and calls out from addresses you cannot pin down in advance, so authenticate the trunk with a username and password rather than an IP allow-list. Go to Credentials List and click + Add Credential. Note the username and password - Vobiz stores the password hashed and does not display it again after creation. See Credentials List for the full walkthrough.

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Step 2: Create the outbound trunk

Go to Outbound Trunks and click + Create New Trunk. Attach the credential from Step 1 under Credentials.
Vobiz outbound trunk detail showing the SIP domain and an attached credentials list
Attach the credential to the trunk. Without either a credential or an IP ACL, the trunk has no way to authenticate traffic from Smallest AI.

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Step 3: Copy the SIP domain

The trunk details panel shows a SIP Domain in the form <trunk-id>.sip.vobiz.ai. Copy it - this is the SIP termination URL that Smallest AI sends outbound calls to. Each trunk gets its own domain and it is never shared.

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Step 4: Import the number in Smallest AI

In the Smallest AI dashboard, open Phone Numbers, choose Add phone number, and select the SIP Trunking method rather than Rent a number.
Smallest AI Import SIP number dialog with fields for phone number, SIP termination URL, SIP authentication details, and SIP origination URL
Although Smallest AI marks the authentication fields optional, this setup needs them - they are what the Vobiz trunk checks. Click Import number. Outbound is now wired.

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Part 2: Inbound calls

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Step 5: Copy the SIP origination URL

The same Smallest AI dialog shows a read-only SIP origination URL, for example sip:5rdbhjuwtlk.sip.livekit.cloud. Copy it with the icon on the right.

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Step 6: Create the origination URI in Vobiz

Go to Origination URIs and create a URI pointing at the Smallest AI address.
Vobiz Create Origination URI dialog with the Smallest AI SIP address and UDP transport selected
Remove the sip: prefix. Smallest AI presents the value as sip:5rdbhjuwtlk.sip.livekit.cloud, and the Vobiz URI field takes domain or domain:port. Paste 5rdbhjuwtlk.sip.livekit.cloud instead.

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Step 7: Create the inbound trunk

Go to Inbound Trunks and create a trunk with the origination URI from Step 6 as its Primary URI.
Vobiz inbound trunk detail showing the primary URI configuration and an empty linked numbers list
Recording, transcription, and webhooks are available on this screen and are all optional. See Callbacks for the webhook payloads. A new trunk starts with Linked Numbers (0). Click Link Numbers, select your Vobiz number, and confirm.
Vobiz inbound trunk showing one linked phone number under the primary URI configuration
The count updates to Linked Numbers (1) and inbound routing is live.

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Test the integration

  • Inbound - call your Vobiz number. The Smallest AI agent should answer.
  • Outbound - trigger a call from Smallest AI to your own phone.
Check Call Logs in the Vobiz Console to see both legs.

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Troubleshooting

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Outbound calls are rejected with a 401 or 403

The trunk is not accepting the credentials. Confirm the username and password in Smallest AI match the Vobiz credential exactly, and that the credential is attached to the outbound trunk and set to Active.

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Outbound calls do not reach Vobiz

Check the SIP termination URL is the trunk’s own SIP domain, in the form <trunk-id>.sip.vobiz.ai. Each trunk has a distinct domain.

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The origination URI is rejected when saving

Remove the sip: prefix. The field takes domain or domain:port.

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Inbound calls ring but never reach the agent

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

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Next steps

Outbound Trunks

Trunk settings, recording, and webhooks

Credentials List

Create and rotate SIP credentials

Inbound Trunks

Route inbound calls to your agent

IP Whitelisting

Vobiz SIP signaling and RTP ranges