> ## Documentation Index > Fetch the complete documentation index at: https://cntillion.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # AI phone answering on your own Twilio number > What an AI receptionist should do on a call, what callers expect, and when to pass the call to a person. Learn the basics, then put an agent on your number. GuideAI phone answering on your own number, with your knowledge and your rules. Many of the calls that matter most arrive when nobody can pick up: during lunch, after closing, while the one person at the front desk is with a customer. AI phone answering puts an agent on the line for those calls. It answers in a natural voice, from what your business knows, and passes the call on when a person should take it. This guide covers what a good phone agent does, then how to put one on your number with Centillion. ## What an AI phone agent does An AI phone agent is closer to a receptionist than to a phone menu. A menu asks the caller to press 2 for billing and hopes the question fits a box. An agent listens to the question in the caller's own words, answers it, and asks a follow-up when it needs one. On a typical call it: * Picks up at once, with a greeting that names your business. * Answers questions about hours, prices, policies and services from your own material. * Takes an action when it is allowed to, such as looking up a record or sending a text with a link. * Moves the call to a person, or tells the caller who to call, when the question is outside its job. The useful way to think about it is as a representative of your business who happens to be on the phone: it knows your products and your rules, and it acts inside them. ## What callers expect Phone is less forgiving than chat. A caller cannot scroll back, skim, or wait while a page loads. A few habits make the difference: * **Short answers.** One or two sentences, then stop. A list of six options read aloud is lost by the fourth. * **Let them interrupt.** People cut in on the phone. The agent should stop talking and listen. Two workflow lines are the exception: the message before a phone transfer and an End step's closing message. The agent finishes both, so the caller always hears who they are being put through to, or how the call ends. * **Their language.** If the caller answers in another language, answer in that one. * **No dead air.** When the agent needs a moment to look something up, it should say so. * **A straight answer about who is on the line.** If a caller asks whether they are talking to a person, tell the truth. Write these into the agent's instructions and test them on real calls before customers hear them. ## When a person should take the call Some calls should not stay with an agent. Decide in advance which ones, and write it down: * A caller who asks for a person, twice. * Anything urgent or safety-related. * A complaint where the caller is upset and the facts are unclear. * A decision that costs money and sits outside your written policy, such as a refund exception. * After hours, anything that cannot wait until morning. For each, decide where the call goes: a colleague's number, an on-call line, or a callback the next working day. Then decide what the agent says while it hands over. The worst version of a handoff makes the caller repeat everything; the best version starts where the agent stopped. ## What to watch for * **Your number stays yours.** Customers already know your number. Putting an agent on it should not mean changing it. * **Cost per minute.** Phone calls cost more than chat messages because voice is billed by the minute. Keep calls focused and let the agent end a call once the question is answered. * **Calls at once.** A busy hour can bring several calls together. Check how many your setup can take at the same time. * **Read the calls.** Every week, read a sample of transcripts. They show what callers ask that your material does not answer yet. * **Calling out is different.** Answering calls is one thing; phoning customers is regulated separately. See [AI outbound calling](https://cntillion.com/docs/guides/ai-outbound-calling.md). ## Set it up in Centillion Centillion's phone agent picks up inbound calls on your numbers with the voice and greeting you chose, and answers with the same instructions and knowledge as in chat. It needs the Standard plan or above and the Owner or Member role. Import a number from your own Twilio account or connect your provider's SIP trunk. The number stays with your provider; Centillion routes its calls to the agent. The [phone numbers guide](https://cntillion.com/docs/channels/phone.md) covers both options. Your workspace's **Phone Numbers** page holds the inventory. You can import a number there before choosing its agent, or import directly from an agent's **Channels → Phone** page and assign it in the same step. **1. Choose the voice and greeting** Open your agent's **Agent**. Pick the voice and the language the call opens in, and write the **First message → Call** the agent greets callers with. Save. ![Agent configuration with the selected voice, language and First message](https://mintcdn.com/centillion/n9koGqutqlVBNAYF/images/channels/phone-02-voice-settings.webp?fit=max\&auto=format\&n=n9koGqutqlVBNAYF\&q=85\&s=af9b619b76c162db51a5f1db5c1414f5) Choose the voice and language on Agent. **2. Open the Phone channel** Open the agent's **Channels** page and choose **Phone**. Click **Add number**. If the workspace already has a number available, select it to assign it to the agent. ![Phone channel card with one active number and Twilio or SIP trunking support](https://mintcdn.com/centillion/NWIZsx75A68vBwc-/images/channels/phone-01-channel-card.webp?fit=max\&auto=format\&n=NWIZsx75A68vBwc-\&q=85\&s=a6bcad57c1592d94ec132f19fbc8a29b) The Phone card shows how many numbers are active for the agent. **3. Import a number if needed** Choose **From Twilio** in the same menu. Enter a label, the phone number in international format, and your Twilio **Account SID** and **Auth Token**. Centillion checks that you own the number and that it can take voice calls, then imports it and assigns it to this agent. For another phone provider, choose **From SIP Trunk** and enter its inbound or outbound settings. The [phone numbers guide](https://cntillion.com/docs/channels/phone.md) explains what you need from your provider. **4. Call it** Call the assigned number from your own phone. The agent answers with your greeting, and the call shows up under **Conversations** with **Phone** as its source. Assigning a number also turns on voice for the agent. To move it later, open **Phone Numbers** at workspace level and choose its new agent. Each number has one assigned agent at a time. To connect a new number, [import it from your Twilio account or SIP provider](https://cntillion.com/docs/channels/phone.md). For help with an [existing Centillion Labs rental](https://cntillion.com/docs/channels/phone-numbers-from-centillion.md), including release or business verification, contact the Centillion Labs team. ### Passing calls to a person The live chat handoff from the helpdesk does not run on phone calls. To move a caller to a person, turn on [Transfer to number](https://cntillion.com/docs/agents/system-tools.md#transfer-to-number) under the agent's **Tools** and add a rule, or add a **Phone number transfer** node to the agent's [workflow](https://cntillion.com/docs/agents/releases-and-workflows.md). Either one moves the call to a phone number or SIP address. Enter a fixed destination, or choose a conversation variable when a business system decides who should answer. For example, map an HTTP tool's `transfer_number` response into a variable and select it as the destination. Post-dial digits, such as an extension, can come from a variable the same way. The value is checked before the call moves. A missing, invalid or sensitive value leaves the caller in the conversation. With **SIP REFER**, you can pass custom `X-` headers and **User-to-User** data to the receiving phone system. Header values can be fixed or read from a variable. User-to-User data supports `{{variable}}` placeholders and an optional protocol discriminator. Your provider and receiving system must support the fields you use. Sensitive variables cannot be sent. Caller ID follows your trunk settings. A number bought through Centillion transfers only to numbers in its own country that are not premium-rate; a number from your own Twilio account can also transfer to a SIP address. Conditions on the workflow decide when it is taken, for example an LLM condition such as "the caller asks for a person," or an expression on `system.hour`, which holds the current hour in UTC, for after-hours routing. When the agent cannot answer, it can offer the caller a callback or the information by message, and record the request as a Helpdesk ticket. This needs Helpdesk on and the **Escalations** tool under **Tools** turned on with **Phone** among its channels and no required fields. Phone is off there by default. Every call is also saved under **Conversations**, so your team can read what was said and follow up. ### Good to know * **Calls at once.** Standard allows ten concurrent voice calls, Pro twenty, across the workspace. * **Credits.** Voice uses six credits per commenced connected minute, plus the model requests. * **One agent per number.** A number belongs to one agent at a time. * **Languages.** The agent opens in the language you saved, and answers in the caller's language if they speak another one. * **Texting customers.** With Twilio connected, the **Twilio** tool under **Tools** lets the agent send an SMS in chat. It does not run during a call. ## Questions ### Do I have to change my phone number? No. Import an existing Twilio number or connect a SIP trunk from your phone provider. The number stays with your provider and Centillion routes its calls to the assigned agent. ### What does the caller hear first? A workflow opening takes precedence. Otherwise, a permitted initiation override can replace the usual **First message → Call** from **Agent**. Leave that field blank and the agent waits for the caller to speak. You can use one agent for both call directions and fetch caller context before it speaks. See [Personalization](https://cntillion.com/docs/agents/personalization.md) for setup and the order of precedence. Calls open without a fixed notice. Include any required AI, transcription or recording [disclosure](https://cntillion.com/docs/agents/disclosure-requirements.md) in every opening you use, and turn off **Interruptible** if it must play in full. ### Can the agent transfer a call to my team? Yes, through a **Phone number transfer** node in the agent's workflow, which moves the caller to a fixed number or SIP address, or one returned by a tool and saved in a conversation variable. The live chat handoff in Helpdesk does not run on calls, but the agent can take a callback request as a ticket when the **Escalations** tool has **Phone** turned on. ### Does the agent know the same things as my website chat? Yes. It follows the same instructions and knowledge as in chat. Chat-only tools, such as Twilio texting, do not run on calls. One agent answers every channel you connect; [What Centillion is](https://cntillion.com/docs/introduction.md) gives the overview. ### Which plan do I need? Standard or above, which includes telephony and voice. Each connected minute also uses credits from the workspace balance. ## Try it Import one number, assign it, and call it from your own phone. The transcript is under **Conversations** when you hang up. > [card] [Start free](https://app.cntillion.com/sign-up?utm_source=docs\&utm_medium=article\&utm_campaign=guides-ai-phone-answering) > > Start on the Free plan, or take a seven-day trial of a paid plan. Your agent is live on your site in an afternoon. > [card] [Book a demo](https://cal.com/patrick-turricelli-smgfks/15min?utm_source=docs\&utm_medium=article\&utm_campaign=guides-ai-phone-answering) > > Fifteen minutes with the team, on your own use case. Or ask the assistant on this page. ## Related > [card] [Phone numbers](https://cntillion.com/docs/channels/phone.md) > > Import Twilio or SIP trunk numbers and choose which agent answers. > [card] [WhatsApp AI agent](https://cntillion.com/docs/guides/whatsapp-ai-agent.md) > > The same agent on WhatsApp, inside Meta's rules. > [card] [Workflows](https://cntillion.com/docs/agents/releases-and-workflows.md) > > Transfer nodes, conditions and per-step voices for calls. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.