SIP Integration

Connect your existing PBX, contact center, or SIP provider to OpenCX so AI agents can answer and make calls through your phone numbers and infrastructure.

Don’t have your own SIP infrastructure? You don’t need it. OpenCX can provision phone numbers for you directly — just create a phone agent in one API call and you’re done. This guide is for teams that want to bring their own telephony.

How it works

┌─────────────┐     SIP INVITE      ┌───────────────┐     routes to     ┌──────────────┐
│  Your PBX /  │ ─────────────────▶ │  OpenCX SIP    │ ──────────────▶ │  AI Phone    │
│  SIP Provider│ ◀───────────────── │  Endpoint      │ ◀────────────── │  Agent       │
└─────────────┘     RTP media       └───────────────┘                  └──────────────┘

You create an inbound SIP trunk — OpenCX gives you a SIP endpoint + credentials.
You point your PBX at that endpoint.
When a call comes in, OpenCX routes it to the right AI agent based on the dialed number or a SIP header.
For outbound calls, you create an outbound SIP trunk with your provider’s credentials and OpenCX dials out through it.

Prerequisites

Before you start, make sure you have:

An OpenCX API key (find it in Settings → API Keys)
At least one verified phone number (verify numbers in the dashboard or via API)
Your SIP provider credentials (if you want outbound calling)

All examples below use curl. Replace $API_KEY with your API key.

Step 1: Create an AI phone agent

Every call needs an agent to answer it. Create one:

curl -X POST https://api.open.cx/phone \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Support Agent",
    "type": "inbound",
    "language": "en",
    "first_message": "Hi, thanks for calling! How can I help you today?",
    "use_org_knowledgebase": true
  }'

Save the returned id — you’ll need it in the steps below. We’ll call it $AGENT_ID.

You can also set voice_id (browse options with GET /phone/voices), handoff_phone_number for human escalation, and actionIds to let the agent call your APIs during conversations.

Step 2: Set up inbound calling (receive calls)

Create the inbound trunk

curl -X POST https://api.open.cx/phone/sip/inbound-trunk \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "phone_numbers": ["+15551234567"],
    "krisp_enabled": true
  }'

If you omit phone_numbers, OpenCX uses all your verified numbers automatically.

The response contains everything you need to configure your PBX:

{
  "id": "a1b2c3d4-...",
  "sip_endpoint": "sip.opencx.example.com",
  "auth_username": "org_abc123",
  "auth_password": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
  "phone_numbers": ["+15551234567"],
  "krisp_enabled": true,
  "agent_id_header": "X-OPENCX-AGENT-ID"
}

Configure your PBX

In your PBX or SIP provider, create a trunk pointing to the OpenCX SIP endpoint:

Setting	Value
SIP Server / Registrar	`sip_endpoint` from the response
Username	`auth_username` from the response
Password	`auth_password` from the response
Transport	UDP (default) or TCP

Route calls to a specific agent

By default, OpenCX routes inbound calls based on the dialed phone number. You can also target a specific agent by setting a SIP header on your PBX:

X-OPENCX-AGENT-ID: <your-agent-id>

This is useful when multiple agents share a phone number.

Assign inbound numbers to the agent

Tell OpenCX which phone numbers should route to your agent:

curl -X PUT https://api.open.cx/phone/sip/agents/$AGENT_ID/inbound-numbers \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "phone_number_ids": ["phone-number-verification-id"]
  }'

Use GET /phone/sip/agents/$AGENT_ID/config to see the agent’s current inbound numbers and outbound trunk at any time.

Step 3: Set up outbound calling (make calls)

Create an outbound trunk

Provide your SIP provider’s credentials:

curl -X POST https://api.open.cx/phone/sip/outbound-trunks \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Twilio Outbound",
    "host": "sip.twilio.com",
    "port": 5060,
    "username": "your-sip-username",
    "password": "your-sip-password",
    "caller_number": "+15551234567",
    "transport": "udp"
  }'

Save the returned id — we’ll call it $TRUNK_ID.

Assign the trunk to your agent

curl -X PUT https://api.open.cx/phone/sip/agents/$AGENT_ID/outbound-trunk \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "trunk_id": "'$TRUNK_ID'"
  }'

Make an outbound call

Now your agent can call out:

curl -X POST https://api.open.cx/phone/outbound-call \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "phone_agent_id": "'$AGENT_ID'",
    "phone_number": "+15559876543"
  }'

The call goes through your SIP provider, using the caller ID you configured on the outbound trunk.

Step 4: Set up call transfers (optional)

Let your AI agent transfer live calls to human teams or other destinations.

Create a transfer destination

curl -X POST https://api.open.cx/phone/sip/transfer-destinations \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "Support Team",
    "type": "phone",
    "value": "+15559999999"
  }'

The type can be "phone" (E.164 number) or "sip" (a SIP URI like sip:[email protected]). Save the returned id — we’ll call it $DEST_ID.

Assign it to your agent

curl -X POST https://api.open.cx/phone/sip/agents/$AGENT_ID/transfer-destinations \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "destination_id": "'$DEST_ID'"
  }'

You can also create and assign in a single call:

curl -X POST https://api.open.cx/phone/sip/agents/$AGENT_ID/transfer-destinations \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "create": {
      "name": "Sales Dept",
      "type": "sip",
      "value": "sip:[email protected]"
    }
  }'

During a call, the AI agent sees the available destinations by name and can initiate a cold transfer when appropriate. Context is preserved via SIP headers (X-OPENCX-SESSION-ID, X-OPENCX-AGENT-ID, X-OPENCX-CONTACT-ID).

Call routing priority

When a SIP call arrives, OpenCX determines which agent handles it in this order:

SIP header — If X-OPENCX-AGENT-ID is set, that agent is used directly.
Phone number assignment — The dialed number is matched against agent inbound number assignments.
Trunk phone number — Matched against the trunk’s phone number list.
Fallback — The first available agent in the organization.

Managing phone numbers on the trunk

After the initial setup, you can add or remove DIDs without recreating the trunk:

# Add a number
curl -X POST https://api.open.cx/phone/sip/inbound-trunk/phone-numbers \
  -H "Authorization: Bearer $API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "phone_numbers": ["+15552223333"] }'

# Remove a number
curl -X DELETE https://api.open.cx/phone/sip/inbound-trunk/phone-numbers/+15552223333 \
  -H "Authorization: Bearer $API_KEY"

# Sync with all verified numbers (adds new, removes unverified)
curl -X POST https://api.open.cx/phone/sip/inbound-trunk/sync \
  -H "Authorization: Bearer $API_KEY"

Full example: end to end

Here’s the complete sequence to go from zero to a working SIP integration:

API="https://api.open.cx"
AUTH="Authorization: Bearer $API_KEY"

# 1. Create an agent
AGENT=$(curl -s -X POST $API/phone \
  -H "$AUTH" -H "Content-Type: application/json" \
  -d '{"name":"Support Agent","type":"inbound","language":"en","first_message":"Hello, how can I help?","use_org_knowledgebase":true}')
AGENT_ID=$(echo $AGENT | jq -r '.id')

# 2. Create inbound trunk (uses all verified numbers)
TRUNK=$(curl -s -X POST $API/phone/sip/inbound-trunk \
  -H "$AUTH" -H "Content-Type: application/json" \
  -d '{"krisp_enabled":true}')
echo "Configure your PBX with:"
echo $TRUNK | jq '{sip_endpoint, auth_username, auth_password}'

# 3. Create outbound trunk
OUT=$(curl -s -X POST $API/phone/sip/outbound-trunks \
  -H "$AUTH" -H "Content-Type: application/json" \
  -d '{"name":"My SIP Provider","host":"sip.provider.com","username":"user","password":"pass","caller_number":"+15551234567"}')
OUT_ID=$(echo $OUT | jq -r '.id')

# 4. Assign outbound trunk to agent
curl -s -X PUT $API/phone/sip/agents/$AGENT_ID/outbound-trunk \
  -H "$AUTH" -H "Content-Type: application/json" \
  -d "{\"trunk_id\":\"$OUT_ID\"}"

# 5. Create and assign a transfer destination
curl -s -X POST $API/phone/sip/agents/$AGENT_ID/transfer-destinations \
  -H "$AUTH" -H "Content-Type: application/json" \
  -d '{"create":{"name":"Human Support","type":"phone","value":"+15559999999"}}'

# Done! Your agent can now receive, make, and transfer calls.
echo "Agent $AGENT_ID is ready."

API Reference

Inbound Trunk

Let the AI agent answer calls on your existing phone numbers. You point your PBX or SIP provider at OpenCX and incoming calls are handled automatically.

Create Inbound Trunk

Provision SIP endpoint + credentials

Get Inbound Trunk

Retrieve SIP credentials

Delete Inbound Trunk

Remove inbound trunk

Sync Phone Numbers

Sync with verified numbers

Add Phone Numbers

Add DIDs to trunk

Remove Phone Number

Remove a DID

Outbound Trunks

Let the AI agent make calls through your own SIP provider. Provide your provider’s credentials once, then any agent can dial out with your caller ID.

List Outbound Trunks

List all outbound trunks

Create Outbound Trunk

Create with SIP provider credentials

Update Outbound Trunk

Update trunk name

Delete Outbound Trunk

Delete outbound trunk

Agent SIP Configuration

Wire everything together — assign which phone numbers route to which agent, and which outbound trunk each agent uses to dial out.

Get Agent Config

View inbound numbers + outbound trunk

Set Inbound Numbers

Assign inbound numbers

Set Outbound Trunk

Assign outbound trunk

Phone Transfer Destinations

Define where the AI agent can transfer live calls — a support team’s phone number, a sales department’s SIP URI, etc. Assign them per-agent to control who can transfer where.

List Destinations

List org destinations

Create Destination

Create phone or SIP destination

Update Destination

Update a destination

Delete Destination

Delete a destination

List Agent Destinations

See agent’s assigned destinations

Assign to Agent

Assign destination to agent

Remove from Agent

Unassign from agent

Overview

Blocklist

Autopilot

Organization

Contacts

Sessions

AI Phone Agents

AI Email

AI WhatsApp

AI Actions

AI Outbound Sequencing

AI Training

Customer Insights

Teams

CSAT

Redaction

Crawl

Tags

Office Hours

Handoff Analytics

Workflows

Webhooks

​How it works

​Prerequisites

​Step 1: Create an AI phone agent

​Step 2: Set up inbound calling (receive calls)

​Create the inbound trunk

​Configure your PBX

​Route calls to a specific agent

​Assign inbound numbers to the agent

​Step 3: Set up outbound calling (make calls)

​Create an outbound trunk

​Assign the trunk to your agent

​Make an outbound call

​Step 4: Set up call transfers (optional)

​Create a transfer destination

​Assign it to your agent

​Call routing priority

​Managing phone numbers on the trunk

​Full example: end to end

​API Reference

​Inbound Trunk

Create Inbound Trunk

Get Inbound Trunk

Delete Inbound Trunk

Sync Phone Numbers

Add Phone Numbers

Remove Phone Number

​Outbound Trunks

List Outbound Trunks

Create Outbound Trunk

Update Outbound Trunk

Delete Outbound Trunk

​Agent SIP Configuration

Get Agent Config

Set Inbound Numbers

Set Outbound Trunk

​Phone Transfer Destinations

List Destinations

Create Destination

Update Destination

Delete Destination

List Agent Destinations

Assign to Agent

Remove from Agent

How it works

Prerequisites

Step 1: Create an AI phone agent

Step 2: Set up inbound calling (receive calls)

Create the inbound trunk

Configure your PBX

Route calls to a specific agent

Assign inbound numbers to the agent

Step 3: Set up outbound calling (make calls)

Create an outbound trunk

Assign the trunk to your agent

Make an outbound call

Step 4: Set up call transfers (optional)

Create a transfer destination

Assign it to your agent

Call routing priority

Managing phone numbers on the trunk

Full example: end to end

API Reference

Inbound Trunk

Outbound Trunks

Agent SIP Configuration

Phone Transfer Destinations