# Connect Twilio (Elastic SIP Trunking) Keep your phone numbers in your own Twilio account and let VINSI AI agents answer and make calls on them. Created: August 26, 2025 Updated: September 18, 2026 ## Overview A Twilio Elastic SIP Trunk connects your Twilio numbers to VINSI in both directions: Twilio sends incoming calls to VINSI (**origination**), and VINSI sends the AI's outgoing calls and transfers out through Twilio (**termination**). The number stays in your Twilio account and on your Twilio bill. Not on Twilio? See [Connecting Your Phone System](https://docs.vinsi.ai/phone-connections/overview) for the other options. ## Before You Start - A Twilio account with at least one voice-capable US or Canada number. - A VINSI AI agent to answer the number. See [Create an AI Phone Agent](https://docs.vinsi.ai/ai-phone-agents/create-agent). - Open VINSI's **Phone Numbers** page and click **Add SIP Trunk**. The **Configure SIP Trunk** window shows your **Origination SIP URI** under _Inbound Call Setup_ — keep it open, you'll need it in step 3. ## 1\. Create the Trunk 1. Log in to the [Twilio Console](https://console.twilio.com). 2. Find **Elastic SIP Trunking** in the left menu (or search for it) and click **Manage** → **Trunks**. 3. Create a new trunk and give it a name you'll recognise, such as _VINSI AI_. 4. Under **General Settings**, turn on **Call Transfer (SIP REFER)** so the AI can hand calls to your team, and **Call Recording** if you want Twilio to keep its own recordings. 5. Click **Save**.  ## 2\. Termination (Outbound) This is the address VINSI uses to send calls out through Twilio. 1. Open the trunk's **Termination** tab. 2. Choose a **Termination SIP URI**, for example `vinsi-acme.pstn.twilio.com`. Note it down — this is the value for VINSI's **SIP Termination URI** field. 3. Under **Authentication**, create a **Credential List** with a username and password, and attach it to the trunk. 4. Click **Save**. **Use a Credential List, not an IP Access Control List.** VINSI's outgoing calls don't always come from the same IP address, so IP-only authentication will reject some calls. Save the password somewhere safe — Twilio won't show it again.  ## 3\. Origination (Inbound) This tells Twilio where to send calls that come in on your number. 1. Open the trunk's **Origination** tab and click **Add new Origination URI**. 2. Paste the **Origination SIP URI** from VINSI's Configure SIP Trunk window. Keep the `sip:` at the start. 3. Set **Priority** to **1** and **Weight** to **1**. 4. Click **Add**.  ## 4\. Add Your Number 1. Open the trunk's **Numbers** tab and click **Add a Number**. 2. Pick an existing Twilio number, or buy one. Calls to it now go through the trunk instead of any webhook it used before.  ## 5\. Connect It in VINSI Back in VINSI's **Configure SIP Trunk** window, fill in: | Field | What to enter | | ------------------- | ---------------------------------------------------------------------------------------------------- | | Trunk Name | Any name, e.g. _Twilio – Main line_. | | Phone Number | Your Twilio number in full format, e.g. +18005551234. | | SIP Termination URI | Your Twilio termination address from step 2 with sip: in front, e.g. sip:vinsi-acme.pstn.twilio.com. | | SIP Username | The Credential List username from step 2. | | SIP Password | The Credential List password from step 2. | 1. Click **Configure Trunk**. The number appears in your list. 2. Assign it to an agent. See [Setting Up Phone Numbers](https://docs.vinsi.ai/ai-phone-agents/setting-up-phone-numbers). ## 6\. Test - **Incoming:** call the number from your mobile. The AI agent should answer. - **Outgoing:** open the agent and click **Call Me** to have the AI ring your phone. - **Transfer:** ask the AI to transfer you, and check the call reaches the right person. Each test call appears in **Call Logs** with its recording and transcript. ## Troubleshooting | Problem | Check | | ------------------------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | Incoming calls don't reach the AI | The number is on the trunk's Numbers tab; the Origination URI matches VINSI's exactly, including sip:; the number is assigned to an agent in VINSI. | | The AI can't call out | The Credential List is attached to the trunk's Termination; the username and password in VINSI match it; the Termination URI in VINSI matches Twilio's, with sip: in front. | | Calls to some countries fail | Turn those destinations on in Twilio's **Voice Geographic Permissions**. | | Transfers don't connect | **Call Transfer (SIP REFER)** is enabled in the trunk's General Settings. | | _Please enter a valid E.164 format phone number_ | Enter the number as +1 followed by 10 digits. The form takes US and Canada numbers. | | _Please enter a valid SIP URI_ | Start the Termination URI with sip:, with no spaces, e.g. sip:vinsi-acme.pstn.twilio.com. |