OpenAI SIP integration brings GPT-4o Realtime capabilities to your phone system, enabling ultra-low latency voice conversations with advanced AI. This guide covers setup and configuration for OpenAI’s SIP platform.
Why Choose OpenAI SIP? #
GPT-4o Realtime Integration #
- Ultra-Low Latency – Near-instant responses powered by GPT-4o Realtime API
- Natural Conversations – Advanced language understanding and context awareness
- Streaming Audio – Real-time audio processing without transcription delays
- Rich Context – Full GPT-4o capabilities including reasoning and knowledge
WebRTC Technology #
OpenAI SIP uses browser-to-browser WebRTC connections, providing high-quality audio with minimal infrastructure overhead.
Important Limitations #
Before proceeding, understand these key limitations:
Inbound Only #
- ✓ Incoming calls supported
- ✗ Outbound calls NOT supported
- ✗ Voice campaigns NOT available
Natural Agents Only #
- Works with “Natural” type agents
- Structured/workflow agents not compatible
- Agent must use conversational approach
No Server Recordings #
- Calls use direct WebRTC browser connections
- No server-side call recordings available
- Transcripts available from OpenAI API
- Use ElevenLabs SIP if recordings are required
Project-Level Provisioning #
- Configuration applies to entire OpenAI project
- All phone numbers share same settings
- Less granular control than ElevenLabs
Prerequisites #
Required Items #
- OpenAI account with API access
- OpenAI Project ID
- OpenAI API Key with appropriate permissions
- Phone number from a SIP provider
- VoxPria account with SIP features enabled
Getting OpenAI Credentials #
- Log into OpenAI Platform
- Navigate to Settings → Organization
- Create or select a Project
- Note your Project ID (found in project settings)
- Generate an API Key with Realtime API permissions
- Copy both values for use in VoxPria
Step-by-Step Setup #
1. Configure Webhook in OpenAI Platform #
OpenAI requires a webhook endpoint to notify VoxPria of incoming calls.
Get Your Webhook URL:
Your unique webhook URL is:
`
https://your-voxpria-domain.com/api/v1/sip/openai/webhook
`
Configure in OpenAI:
- Go to OpenAI Platform
- Navigate to your Project Settings
- Find Realtime API or Webhooks section
- Add new webhook endpoint
- Enter your VoxPria webhook URL
- Select event types:
call.started,call.ended,call.updated - Save the webhook secret – you’ll need this for VoxPria
2. Create OpenAI SIP Trunk in VoxPria #
Set up the connection to OpenAI’s SIP infrastructure.
- In VoxPria, navigate to Phone Numbers → SIP Trunks
- Click Create Trunk
- Select OpenAI as the provider type
- Fill in trunk details:
Trunk Name
- Descriptive name like “OpenAI Production Trunk”
- Helps identify when managing multiple trunks
OpenAI Project ID
- Paste your Project ID from OpenAI Platform
- Format:
proj_xxxxxxxxxxxxxxxxxxxxx
OpenAI API Key
- Paste your API key with Realtime permissions
- Format:
sk-proj-xxxxxxxxxxxxxxxxxxxxx - Keep secure – only shown during creation
Webhook Secret
- Paste the webhook secret from OpenAI
- Used to verify incoming webhook requests
- Critical for security – see security section below
SIP Server
- Pre-configured for OpenAI’s infrastructure
- No changes needed
- Click Create Trunk to save
3. Import Phone Numbers #
Add your SIP provider’s phone numbers.
- Go to Phone Numbers in VoxPria
- Click Import Number
- Enter number in E.164 format (e.g.,
+12125551234) - Select your OpenAI trunk
- Choose OpenAI as the engine
- Click Import
Important Notes:
- Number must exist with your SIP provider
- Provider must route calls to OpenAI’s SIP endpoints
- Check with your provider for routing configuration
4. Provision Your OpenAI Project #
Unlike ElevenLabs, OpenAI requires project-level provisioning.
- In VoxPria, go to SIP Trunks
- Find your OpenAI trunk
- Click Provision Project
- Wait for provisioning to complete
- All phone numbers on this trunk are now active
Note: This provisions your entire OpenAI project. Any additional numbers imported later will automatically use this configuration.
5. Configure Your SIP Provider #
Your SIP provider must route calls to OpenAI’s endpoints.
Typical Configuration:
- Log into your SIP provider dashboard
- Find your phone number routing settings
- Set destination to OpenAI’s SIP domain
- Configure authentication if required
- Set transport to TLS (recommended)
- Save configuration
Consult Your Provider:
Each SIP provider has different configuration interfaces. Common providers include:
- Twilio
- Telnyx
- Bandwidth
- Vonage
Refer to their documentation for specific routing setup instructions.
6. Assign Natural Agents #
Connect phone numbers to compatible agents.
- Edit your phone number in VoxPria
- Select a Natural type agent from dropdown
- Important: Only natural/conversational agents work with OpenAI SIP
- Configure optional settings:
- First Message – Initial greeting
- Max Duration – Call time limit
- Language – Conversation language
- Click Save Changes
7. Test Your Setup #
Verify the complete integration.
Make a Test Call:
- Use your mobile phone to call your configured number
- Call should connect through your SIP provider to OpenAI
- VoxPria receives webhook and connects your agent
- Have a conversation to test latency and quality
Check Call Logs:
- Navigate to Call Logs in VoxPria
- Find your test call
- Review transcript from OpenAI
- Check for any error messages
Webhook Security Configuration #
Webhook security is critical for OpenAI SIP. Without proper configuration, unauthorized parties could trigger fake calls.
Why Webhook Security Matters #
Without webhook secret verification:
- Anyone who knows your webhook URL could send fake call events
- Potential unauthorized access to your agents
- Security breach and privacy concerns
- Fraudulent usage charges
With proper verification:
- All webhook requests are cryptographically signed
- Invalid signatures automatically rejected
- Only authentic OpenAI requests processed
- Your system remains secure
Configuring Webhook Secret #
During Trunk Creation:
- When creating your OpenAI trunk, paste webhook secret
- VoxPria stores it securely
- All incoming webhooks validated using HMAC-SHA256
- Invalid requests return HTTP 401 Unauthorized
Updating Webhook Secret:
- Edit your OpenAI trunk in VoxPria
- Update the webhook secret field
- Click Save Changes
- Re-provision project to apply changes
Verifying Security #
Test Security:
- Try calling without configured secret (should fail)
- Configure secret and test again (should succeed)
- Change secret in OpenAI but not VoxPria (should fail)
- Update VoxPria to match (should succeed)
Advanced Configuration #
Call Handling Options #
Configure how your agents handle incoming calls.
Max Call Duration:
- Set in seconds (default: 3600 = 1 hour)
- Prevents excessively long calls
- Configurable per phone number
Language Settings:
- Primary conversation language
- Affects speech recognition accuracy
- Set to match your target audience
First Message:
- Custom greeting when call connects
- Keeps conversation flowing naturally
- Test different greetings for best results
Multiple Phone Numbers #
Scale your OpenAI SIP setup with multiple numbers.
All Numbers Share Configuration:
- Single project-level provisioning
- Same webhook endpoint
- Shared API credentials
- Consistent agent behavior
Differentiation:
- Assign different agents to different numbers
- Use custom first messages per number
- Configure different max durations
- Track usage by number in logs
API Integration #
Programmatically manage OpenAI SIP configurations.
Create Trunk via API:
`bash
curl -X POST https://api.voxpria.com/v1/sip/trunks \
-H “Authorization: Bearer YOUR_API_KEY” \
-H “Content-Type: application/json” \
-d ‘{
“name”: “My OpenAI Trunk”,
“provider”: “openai”,
“credentials”: {
“project_id”: “proj_xxxxxxxxxxxxx”,
“api_key”: “sk-proj-xxxxxxxxxxxxx”,
“webhook_secret”: “whsec_xxxxxxxxxxxxx”
}
}’
`
Import Number via API:
`bash
curl -X POST https://api.voxpria.com/v1/phone-numbers/import \
-H “Authorization: Bearer YOUR_API_KEY” \
-H “Content-Type: application/json” \
-d ‘{
“phone_number”: “+12125551234”,
“trunk_id”: “trunk_abc123”,
“engine”: “openai”,
“agent_id”: “agent_def456”
}’
`
Troubleshooting #
Webhook Not Receiving Events #
Symptoms: Calls don’t trigger VoxPria, no connection to agent
Solutions:
- Verify webhook URL is publicly accessible (not localhost)
- Check webhook secret matches between OpenAI and VoxPria
- Ensure SSL certificate is valid on your domain
- Review OpenAI Platform webhook delivery logs
- Check firewall allows incoming HTTPS traffic
Agent Not Responding #
Symptoms: Call connects but agent doesn’t talk
Solutions:
- Confirm agent type is “Natural” (not structured/workflow)
- Verify agent has valid system prompt configured
- Check OpenAI API key has Realtime API permissions
- Review call logs for specific error messages
- Test agent in VoxPria interface first
SIP Provider Routing Issues #
Symptoms: Calls fail before reaching OpenAI
Solutions:
- Verify provider routes calls to OpenAI SIP endpoints
- Check authentication credentials with provider
- Ensure transport settings match (TLS preferred)
- Review provider’s call logs for rejection reasons
- Contact provider support for routing verification
Webhook Signature Validation Failing #
Symptoms: HTTP 401 errors in OpenAI webhook logs
Solutions:
- Verify webhook secret exactly matches OpenAI’s generated secret
- Check for extra spaces or characters when copying
- Regenerate webhook secret in OpenAI if needed
- Update VoxPria trunk with new secret
- Re-provision project after updating
Poor Audio Quality #
Symptoms: Choppy audio, lag, or connection drops
Solutions:
- Verify your SIP provider supports WebRTC
- Check network quality on caller’s end
- Test from different locations/networks
- Review OpenAI status page for service issues
- Consider switching to ElevenLabs if issues persist
Calls Disconnecting Prematurely #
Symptoms: Calls end unexpectedly mid-conversation
Solutions:
- Check max duration setting isn’t too short
- Verify OpenAI API credits are sufficient
- Review call logs for disconnect reason
- Test with simpler agent prompts
- Monitor OpenAI API usage dashboard
Cost Considerations #
OpenAI Pricing #
- GPT-4o Realtime API – Per-second audio pricing
- API Request Costs – Charged per minute of conversation
- Webhook Delivery – Usually included in API pricing
- Check OpenAI Pricing for current rates
SIP Provider Costs #
- Phone Number Rental – Monthly fees vary by provider and country
- Inbound Minutes – Per-minute charges for incoming calls
- Setup Fees – One-time provider activation costs
VoxPria Fees #
- SIP Feature Access – Included in eligible plans
- No Per-Call Fees – VoxPria doesn’t charge for SIP usage
- Agent Usage – Standard agent interaction charges apply
Best Practices #
Security #
- Always configure webhook secret – Never skip this step
- Use strong, unique secrets for each environment
- Regularly rotate API keys and secrets
- Monitor webhook logs for suspicious activity
- Enable IP allowlisting if provider supports it
Performance #
- Keep agent prompts concise for faster responses
- Test thoroughly before production deployment
- Monitor call quality metrics regularly
- Use VoxPria’s call logs to identify issues early
Reliability #
- Set up health monitoring for webhook endpoint
- Configure alerting for failed webhook deliveries
- Keep SIP provider routing updated
- Test failover procedures periodically
- Maintain documentation of current configuration
Agent Design #
- Use natural, conversational prompts
- Avoid complex structured workflows
- Test conversations extensively
- Optimize for GPT-4o’s strengths
- Keep context concise for better performance
Comparison: OpenAI vs ElevenLabs #
Use OpenAI SIP When: #
- You need ultra-low latency responses
- GPT-4o Realtime capabilities are essential
- Only inbound calls are required
- Transcripts are sufficient (no recordings needed)
- Budget allows for premium API costs
Use ElevenLabs SIP When: #
- You need outbound calling capabilities
- Voice campaigns are required
- Call recordings are essential
- Supporting all agent types
- Cost optimization is important
Next Steps #
- Review API Reference for programmatic control
- Study Troubleshooting Guide for common issues
- Check Security Best Practices for hardening
- Explore FAQ for additional information
Additional Resources #
- OpenAI Realtime API Documentation
- VoxPria API Documentation
- Webhook Security Guide
- SIP Protocol Overview
Need help with OpenAI SIP setup? Contact VoxPria support for expert assistance.
