Using Twilio with Retell AI via SIP Trunking for Voice AI Agents

Follow the steps below to use Twilio with Retell AI via SIP Trunking for Voice AI Agents:

#1 Arrange government-issued IDs for verification.

Telecom is a regulated industry, so using Twilio, Retell AI, or any programmable telecom platform often requires completing country-specific compliance steps before you can fully use the service.

• Verify your identity with a government-issued photo ID (passport, driver’s license, voter ID, etc.)
• Provide proof of address and/or business registration (utility bill, tax notice, company certificate, etc.)
• Create and validate a Regulatory Bundle in Twilio to purchase and activate local phone numbers.
• Verify your identity to make outbound calls in Retell AI.

Upgrading from a trial to a paid Twilio account may also require photo ID verification.

1. Gather your government-issued ID.
2. Have proof of address and/or business registration ready.
3. Prepare clear digital scans/photos for upload during onboarding.

Note: Regulatory requirements vary by country, but preparing these documents early will speed up onboarding and help you get to production faster.

#2 Sign up for the Twilio account.

#2.1 Navigate to https://www.twilio.com/en-us .

#2.2 Click on the 'Start for Free' button.

#2.3 Sign up with your email address and password or via Google login.

#2.4 You will now be asked to verify your phone number by sending a code via SMS or Voice Call.

#2.5 You may be asked about your use case, company details, or development experience. This helps Twilio personalise your setup.

#2.6 Accept Twilio’s terms and privacy policy and finish creating your account.

#2.7 Once registered and verified, you will be directed to the Twilio Console dashboard which looks like the one below:

#3 Upgrade your Twilio account.

#1 A trial account requires verification of non-Twilio phone numbers before you can call or message them. It means on a Twilio trial (free) account, you can only send messages or make calls to phone numbers that you have manually added and verified as "Verified Caller IDs" within your Twilio Console. This restriction is removed when you upgrade.

#2 You are limited to a single Twilio phone number on trial. With a paid account, you can purchase as many numbers (local, toll-free, mobile, worldwide) as needed.

#3 A paid account is designed for production workloads. It allows for higher API limits and faster support for scaling business needs.

#4 Only paid accounts can create subaccounts (needed for client isolation, clear billing, or multi-project management).

#3.1 Navigate to https://console.twilio.com/

#3.2 Click on the ‘Upgrade’ link in your Twilio account:

#3.3 Follow the on-screen instructions. You would need to take a photo of a government-issued ID (like a driver's license, Passport, Voter ID, etc) to verify your identity.

#3.4 Set Identity type to ‘Business use’ and 'Independent Software Vendor (ISV) Reseller, or Partner’:

#3.5 In the next step, provide your business information.

#3.6 Enter your billing information.

#3.7 You will be asked to fund your account. This is usually a minimum first payment (for example, $20).

Note(1): Funding is mandatory. You cannot upgrade without adding a payment method and making an initial deposit.

Note(2): The balance goes into your Twilio account as credits, which you use to pay for calls, texts, numbers, etc. Your balance is used “pay-as-you-go” for Twilio services.

#3.8 Once payment is approved and any required verification is completed, you are upgraded to a full, paid account.

#3.9 Visit the Twilio Payments page to view your payment history or download a printable receipt.

#4 Rename your Twilio account.

Renaming your main Twilio account from the default (e.g., “My first Twilio account”) to something meaningful and unique is a best practice because:

#1 You can instantly recognize your main Twilio account in dashboards, billing statements, and API management UIs especially if you are planning to add subaccounts.

#2 If you manage multiple Twilio accounts (for clients or internal purposes), having clear names helps prevent costly mistakes, like sending live messages from the wrong account or configuring phone numbers in the wrong environment.

#3 The account name often appears in logs, API responses, webhooks, and project documentation. A meaningful name minimizes ambiguity for developers and operations.

#4.1 Once you have upgraded your Twilio account, navigate to Admin > Account Management:

#4.2 Enter your verification code and then click on the ‘Verify’ button:

You should now see a screen like the one below:

#4.3 Change your account name from ‘My first Twilio account’ to ‘Main Twilio account’ or whatever you prefer and then save your changes:

#5 Understand the importance of programmable phone numbers.

Programmable phone numbers are virtual phone numbers that you can fully control with software, usually through an API.

Unlike a regular phone number that’s tied to a SIM card, handset, or fixed line, a programmable number lives in the cloud and can be configured in real time to send/receive calls and messages, trigger code, and integrate with applications.

• Route calls using APIs or custom call-handling logic.
• Trigger webhooks for real-time AI interactions.
• Use SIP trunking to connect with external systems.

Standard phone numbers from traditional carriers (Vodafone, Verizon, Airtel, etc.) are tied directly to their network and devices. They don’t allow you to insert a webhook, SIP endpoint, or third-party platform between the carrier and your phone, which means they can’t provide these advanced capabilities.

AI voice platforms like ‘Retell AI’ cannot connect just any ‘regular’ phone number (like a personal mobile or landline) directly to its AI agents.