For a small office with nobody technical, ElevenLabs Agents and Retell AI are the most practical picks: both let you build the receptionist in a browser by writing what it should say, adding your hours and FAQ, and testing a call before you connect a phone number. Retell has a ready-made receptionist template and can sell you a US or Canadian number, while ElevenLabs connects to a number you hold with a phone provider such as Twilio. The free lesson ElevenLabs: Never Miss an After-Hours Client Call builds one for an accounting firm from a blank agent to a checked test call.
Whichever you pick, a good after-hours receptionist does three things: says it is an AI, answers simple questions from a short document, and takes a clear message (name, number, reason, how urgent) for the morning. It should never give advice, quote prices it is not sure of or promise anything on your behalf.
Which product fits which office?
- ElevenLabs Agents. Write a system prompt and a first message, attach a knowledge base document, publish, then test in the browser and read every call under Conversations. You can import a Twilio number and assign the agent to it for inbound calls. Deciding factor: you want lots of voice choice and a clear call log.
- Retell AI. Start from a Receptionist template or describe the agent in plain words, test it in the browser, then buy a number, port yours or forward to it. Deciding factor: you want a template and the phone number handled in one place.
- Synthflow. A no-code voice agent platform aimed at appointment booking, rescheduling and reminders. Deciding factor: booking is the main job, not message-taking.
- Vapi. A developer platform for voice agents that connects to phone systems and CRMs. Deciding factor: you have a developer, or an agency builds it for you.
Compare the three most common platforms in ElevenLabs vs Vapi vs Retell for voice agents. If you are not sure you need AI at all, AI receptionist vs answering service vs voicemail weighs the three.
How do I set one up?
- Write a one-page document: hours, address, parking, services, how new clients start, and the questions callers ask most.
- Write the rules: say it is an AI, no advice, no prices unless listed, and the steps for taking a message.
- Write the greeting: firm name, the office is closed, this is an AI assistant, the call may be recorded.
- Test five calls in the browser, including one where the caller pushes for advice.
- Connect the number and decide where messages go: email, a shared inbox or a ticket.
- Read every transcript for the first two weeks. The setup checklist has the full list.
What does this look like in a real lesson?
In the ElevenLabs lesson you build "Casey" for a small accounting firm. You choose Blank Agent, paste a system prompt that says Casey is an AI, lists six steps for taking a message and bans tax advice and prices, then add a greeting that says the office is closed and the call may be recorded. You create a knowledge base text with the hours, services and FAQ, publish, and start a test call. Casey answers when the office opens on Monday and whether the firm does payroll, declines to give tax advice about an IRS letter, takes your name, number and Friday deadline, and marks the message urgent. You finish by reading the call's overview and transcript.
Two industry versions show how the rules change: After-Hours Intake for a Law Firm says up front it is not a lawyer and never judges a case, and Coverage FAQ Voice Agent for an Insurance Agency explains coverage only in general terms and refuses to change a policy.
What mistakes should I avoid?
- Hiding that it is an AI. Say it in the greeting, and say the call may be recorded. Recording rules vary by state.
- Letting it advise. Legal, tax, medical and insurance questions go to a person.
- No plan for urgent calls. Decide what counts as urgent and who sees those messages first.
- Never reading the calls. Transcripts show where the prompt needs fixing.
Key takeaways
- ElevenLabs Agents and Retell suit a small office with no developer.
- Synthflow fits booking; Vapi fits a developer build.
- A good receptionist says it is AI, answers from a short document and takes clear messages.
- A person reads every message and every early transcript.
Frequently asked questions
- Can I keep my office phone number?
Usually yes. Retell lets you port or forward your existing number, and ElevenLabs works with numbers you hold with a provider like Twilio. Check with your phone provider before you switch.
- Is an AI receptionist better than an answering service?
It answers instantly and never runs out of staff, but it cannot use judgment. Many offices use AI for routine calls and a person for anything urgent.
- What should it never do?
Give advice, promise appointments it cannot book, quote unlisted prices or collect sensitive numbers like Social Security numbers. The after-hours calls use case covers the guardrails.