Building Blocks vs Agent Platform
Twilio is the telephony layer much of the industry runs on, with phone numbers in 100+ countries and more than 400,000 customer accounts. For voice AI it offers building blocks: Conversation Relay handles speech-to-text, text-to-speech and the call session over a WebSocket, and Media Streams sends raw call audio to your own systems.
The Catch
Twilio does not host the agent. With Conversation Relay, your team brings the LLM, runs the WebSocket server that holds the conversation logic, and builds handoffs to people in your own call-control code.
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Retell is the agent layer. It handles transcription, turn-taking, the LLM, voices and call control in one platform, and it works with Twilio: use Retell numbers that run on Twilio, or connect your existing Twilio numbers over elastic SIP trunking.
- No-code Conversation Flow builder or prompt-based agents
- GPT, Claude and Gemini models, or bring your own LLM
- Cold, warm and agentic warm transfer
- Simulation testing and post-call analysis built in
- HIPAA with a self-serve BAA on every plan
Keep your Twilio numbers. Skip building the agent.
Why Retell is Different
What your team builds on each
Feature, Pricing & Compliance Breakdown
Compare what you would build on Twilio's voice AI building blocks with what comes ready on Retell, from LLM hosting to HIPAA coverage.
Retell is the AI Voice Platform Enterprise Contact Centers Run On
Built to Work With Twilio
Add the agent without changing your carrier
When to Use Each Tool
Use Twilio when you:
- Want to build your own voice agent and control every layer
- Already have engineers running an LLM application
- Need phone numbers across 100+ countries
- Run your contact center on Twilio Flex
Twilio is the right foundation for teams building communications into their own product.
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Use Retell when you:
- Want a production voice agent without hosting the LLM app yourself
- Want to keep Twilio as your carrier and add the agent on top
- Need transfers, IVR navigation and voicemail detection ready to configure
- Need HIPAA coverage without upgrading to a paid edition
Retell is the right choice when the goal is calls handled well, not an agent stack to maintain.
Common  Questions
Revolutionize your call operation with Retell
