Twilio is the telephony layer under a huge share of business phone systems. Retell is the voice AI agent that rides on top of it. Attach Retell to your existing Twilio numbers and SIP trunks, and every call can be answered by an agent that holds a real conversation, takes action in your systems, and transfers to a human when it should.
Retell adds the conversation and decision layer; Twilio carries the call. Together they cover the common voice-agent patterns:
Point a Twilio number, or a whole SIP trunk, at a Retell agent. Callers reach a natural-conversation agent instead of a phone tree, on the number they already know.
Trigger appointment reminders, follow-ups, and confirmations through the API, with the agent handling the conversation and writing results back to your systems.
When a call meets your escalation rules, the agent transfers to a person, a queue, or another number and hands over the context it has already gathered, so the caller does not repeat themselves.
Capture recordings and structured transcripts, then push summaries and outcomes into your CRM, subject to the consent rules you configure.
Retell sits between your Twilio telephony and the language model that runs the conversation. Twilio handles the call media and your numbers; Retell handles speech-to-text, the agent's reasoning and tool calls, and text-to-speech, within the sub-second latency budget a natural phone conversation requires.
You connect your Twilio account, route a number or SIP trunk to your agent for inbound, or call the API for outbound, and configure your transfer and escalation rules. Because you bring your own Twilio, you keep your numbers, your carrier relationship, and your existing telephony configuration.
Provide your Twilio credentials so Retell can attach to your numbers and SIP trunks.
Route an existing Twilio number, or a SIP trunk, to your Retell agent for inbound calls. For outbound, trigger calls through the API.
Set the escalation and warm-transfer rules that decide when the agent hands a call to a human.
Run real call scenarios end to end, confirm recording and logging behave as expected, then move production traffic onto the agent.
Step-by-step configuration lives in the Twilio integration docs. This page is the overview; the docs are the instructions.
With your Twilio numbers on a Retell agent, the vertical use cases follow:
No. You keep your numbers on Twilio. Retell attaches to your existing Twilio numbers and SIP trunks, so you bring your telephony and add a voice AI agent on top of it rather than migrating carriers.
Yes. You define the rules, and the agent performs warm or cold transfers to a human team, another number, or a queue when a call meets your escalation criteria, passing along the context it has already gathered.
Both. Inbound calls to your Twilio numbers can be answered by the agent, and you can trigger outbound calls, such as reminders or follow-ups, programmatically through the API.
Yes. Calls can be recorded, and each conversation produces a transcript and structured summary you can store or push into your CRM, subject to the consent and compliance rules you configure.