Phone numbers - Cartesia Docs

Cartesia supports three ways to connect phone numbers to your agents: Cartesia-provisioned numbers, numbers imported from Twilio, and numbers connected through your SIP carrier. Agent calling rates apply to all three options. Cartesia charges an additional telephony fee only when you use a Cartesia-provisioned number.

Feature	Cartesia numbers	Twilio numbers	SIP trunk numbers
Number origin	US only	Any country available in Twilio	Any country available from your carrier
Inbound calls	✓	✓	✓ with inbound configured
Outbound to US	✓	✓	✓ with outbound configured
Outbound international	✗	✓ at your Twilio cost	Carrier-dependent, with outbound configured
Regional routing	N/A	Configurable	Carrier-dependent
Provisioning	Automatic	Import from Twilio	Import from your carrier
Telephony cost	+$0.014/min add-on	Your Twilio rates apply	Your carrier rates apply

Cartesia numbers

Provision US numbers from Cartesia.

Twilio

Import numbers from your Twilio account.

SIP trunk

Connect numbers from your SIP carrier.

Manage numbers

View and manage every number on the Phone Numbers page in the Playground or through the Phone Numbers API.

Phone numbers page listing numbers in the Playground — Phone numbers in the Playground

Assign an inbound agent

Assigning a phone number to an agent routes inbound calls on that number to the agent. A number is assigned to one agent at a time, and an agent can have several numbers.

Playground
API

Open the phone number’s detail page.
In the Agent card, search for and select your agent.

curl -X PATCH "https://api.cartesia.ai/agents/phone-numbers/YOUR_PHONE_NUMBER_ID" \
  -H "X-API-Key: $CARTESIA_API_KEY" \
  -H "Cartesia-Version: 2026-08-14" \
  -H "Content-Type: application/json" \
  -d '{ "agent_id": "YOUR_AGENT_ID" }'

To unassign, set agent_id to null.

Outbound calls

Any number on your account can place outbound calls, whether or not it is assigned to an agent. Pass its ID as from_number_id when you place an outbound call.

Cartesia numbers

Twilio

SIP trunk

​Manage numbers

​Assign an inbound agent

​Outbound calls

Manage numbers

Assign an inbound agent

Outbound calls