> ## Documentation Index > Fetch the complete documentation index at: https://docs.bland.ai/llms.txt > Use this file to discover all available pages before exploring further. # Twilio > Connect numbers on a Twilio Elastic SIP Trunk to a Bland agent over SIP with Secure Trunking Keep your numbers on a Twilio Elastic SIP Trunk and have a Bland agent answer them. Twilio sends inbound calls to Bland over TLS with SRTP, and Bland places outbound calls through your trunk's termination URI. Your numbers stay on your trunk, and Bland never gets your Twilio API credentials. You can split numbers between Bland and your own PBX. > [!NOTE] > > Want Bland to run calls on your Twilio numbers without any SIP setup? Use [Custom Twilio](https://docs.bland.ai/tutorials/custom-twilio.md) instead. It connects your Twilio account to Bland by API. ## What works * Inbound calls to your agent * Outbound calls from your agent * Transfers from your agent, with SIP REFER ## Prerequisites * A Twilio account with Elastic SIP Trunking, and the numbers you want to use * A Bland account with SIP trunking enabled. If there is no **SIP** tab under **Phone numbers**, contact Bland support ## Configure Twilio **1. Create the trunk** In the Twilio Console, go to **Elastic SIP Trunking**, then **Trunks**, and create a trunk. Name it, for example `Bland`. **2. Turn on Secure Trunking and Call Transfer** Under **General**, turn on **Secure Trunking**. Twilio then rejects any unencrypted call, which matches Bland: TLS signaling and SRTP media. On the same page, turn on **Call Transfer (SIP REFER)**, and transfers to the PSTN if your agent transfers to phone numbers. Leave **Caller ID for Transfer Target** on **Transferee** so the target sees the original caller. **3. Point origination at Bland** Under **Origination**, add an origination SIP URI for your Bland region, with TLS on port 5061: ```text theme={null} sip:us2.sip.bland.ai:5061;transport=tls ``` Use `sip:` with `;transport=tls`, not `sips:`. Use port 5061 exactly: Bland reserves its other SIP ports for its own carrier connections. The other regions are under [Connection endpoints](https://docs.bland.ai/agents/sip-network.md#connection-endpoints). Bland already trusts Twilio's published signaling IPs, so there is nothing to allow-list. **4. Add your numbers** Under **Numbers**, associate the numbers your agent should answer with the trunk. **5. Create termination credentials** Skip this if you only need inbound calls. Under **Termination**, note your termination SIP URI, for example `yourcompany.pstn.twilio.com`. Under **Authentication**, create a **Credential List** with a username and password, and attach it to the trunk. Use a credential list, not an IP access control list. Bland's outbound calls don't come from a fixed set of IPs you can list. ## Configure Bland **1. Open the setup wizard** At **All agents**, go to **Dispatch**, then **Phone numbers**, then the **SIP** tab, and press **Create trunk**. **2. Provider** Pick **Twilio** and enter your termination SIP URI, for example `yourcompany.pstn.twilio.com`. No port needed. The wizard skips the firewall step for Twilio. **3. Authentication** Pick **IP-based**, and leave **Outbound routing** on **Via Bland's carrier**. Under **Outbound call credentials**, enter the username and password from your Twilio credential list. Press **Create trunk**. **4. Numbers** Add each number in E.164 format, for example `+14155550100`. **5. Assign an agent** Under **Phone numbers**, press **Configure** on the number and pick the agent under **Assignment**. You know it worked when a call to the number reaches the agent and shows up on the trunk's **Overview** tab. For outbound, use the number as `from` in [`POST /v1/calls`](https://docs.bland.ai/api-v1/post/calls). ## Caller ID and transfers Twilio only accepts outbound calls whose caller ID is a number on your Twilio account or a verified caller ID, in E.164 format. Place outbound calls from a number on the trunk. The same rule shapes transfers. When Bland bridges a transfer, the target can't see the original caller, because that number isn't on your account. With SIP REFER, Twilio places the transfer itself and shows the original caller. To transfer with REFER, turn on **Hand off via SIP REFER** in the agent's **Transfer Call** node and enter the target in E.164 format. Bland leaves the call once Twilio takes it. Twilio can't transfer to emergency numbers, and plays no early media during a REFER. See [Transfers](https://docs.bland.ai/agents/sip-transfers.md) for every transfer method. ## Common failures > [accordion] Inbound calls don't reach Bland > > Check the origination URI is `sip:.sip.bland.ai:5061;transport=tls`, and that **Secure Trunking** is on. > [accordion] Inbound calls are rejected with 603 Decline > > The number isn't attached in Bland. Attach it on the trunk in E.164 format. > [accordion] Outbound calls are rejected with 401 or 403 > > The username and password in Bland don't match the credential list attached to the trunk. > [accordion] Outbound calls fail with 400 or a caller ID error > > The caller ID isn't a number on your Twilio account, or isn't in E.164 format. Call from a number on the trunk, with the `+`. > [accordion] Transfers fail > > **Call Transfer (SIP REFER)** is off on the trunk, or transfers to the PSTN aren't allowed. Turn both on. > [accordion] The call connects with no audio > > **Secure Trunking** is off. Twilio and Bland both need SRTP with `AES_CM_128_HMAC_SHA1_80`. ## Next steps > [card] [Transfers](https://docs.bland.ai/agents/sip-transfers.md) > > REFER, new INVITE, and warm transfers. > [card] [Custom Twilio](https://docs.bland.ai/tutorials/custom-twilio.md) > > Connect your Twilio account by API instead. Docs for agents: [llms.txt](https://docs.bland.ai/llms.txt) This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.