How to build a voice AI agent for your business

Step 3: Write the script and the rules

The script starts and ends the call. Rules set its limits. Platforms often call this text the prompt.

Start with a short, honest greeting:

"Thanks for calling [business name]. I'm an AI assistant. I can answer questions, take a message, or get [your name]. How can I help?"

Then write the rules in short lines. For example:

• Only use facts from the approved list.
• If you do not know, say so. Offer to take a message.
• Never give a price unless it is on the list.
• Never promise a date, a refund or a fix.
• Get the caller's name and best number before the call ends.
• If the caller asks for a person, transfer the call.
• If the caller is upset, transfer the call.
• If someone may be hurt or in danger, tell them to hang up and call the local emergency number.

End every call the same way. Repeat back the name, number and reason. Say when they will hear back. Only name a time you can keep.

Step 4: Choose a platform and a phone number

Pick a self-serve platform you can set up without code. Look for:

• A per-minute price with every part listed.
• A place to load your facts and your script.
• Call transfer to a real phone number.
• Call records or transcripts you can read later.
• Settings for recording and for how long data is kept.
• A test mode, so you can call it before the public can.

Pick a voice that is clear and calm. Listen to it on a real call before you decide.

Get a new number from the platform, or forward your current line to it. A new number is the safer first test. Your main line stays as it is until you trust the agent.

If you already run your business on GoHighLevel, read about voice agents in GoHighLevel before you add a separate tool.

Step 5: Set up the handoff to you, and a fallback

The agent must help callers reach you.

Decide three things:

1. Where a transfer goes. Pick the number you will really answer, like your cell.
2. When it transfers. Put the triggers in the rules: the caller asks for a person, the caller is upset, the job is one you have not approved, or the call is about a complaint or money owed.
3. What happens if you don't pick up. The agent takes a message and tells the caller when you will call back. If the platform can send that message to you by text or email, turn it on.

If the agent fails, send the line back to your phone. Write down and test that fallback before launch.

Step 6: Decide what it can hear, keep and share

Every call holds a person's voice and words. Make these choices on purpose, before the first real call:

• Say it is an AI. Put it in the greeting. People should know who they are talking to.
• Recording. Decide if calls are recorded. Rules on recording differ by country and by state. Check the rules where you and your callers are before you turn it on.
• Transcripts. Decide who can read them. Keep that list short.
• How long you keep data. Pick the shortest time that still lets you review calls.
• What it must never take. Card numbers, passwords, health details and ID numbers stay off the call. Add a rule: if a caller starts to share these, the agent stops them and offers a call back from you.
• Where the data goes. Read the platform's privacy page.

Step 7: Test it before anyone else can call

Call it yourself, then ask a friend to call. Make at least 20 test calls, and cover this list:

• A plain question from your facts list.
• A question it has no answer for.
• "Can I talk to a person?"
• An upset caller.
• A caller who talks fast, or cuts in while the agent speaks.
• A call from a loud place, like a car.
• A caller who asks for a price.
• A caller who tries to read out a card number.

After each call, read the transcript and ask:

1. Did it say anything that is not in your facts?
2. Did it transfer when the rules said to?
3. Did it get the name and number right?
4. Was the pause before each reply short enough to feel normal?

Fix the facts or the rules, then test again. Go live only after a full round passes. If one test keeps failing, keep that job for yourself.

Step 8: Go live small, then review every week

Start with one slice of calls, like after-hours calls. Keep your main line on your own phone at first.

Each week:

• Read a sample of call transcripts.
• Look for wrong answers, missed transfers and lost messages.
• Add new questions and answers to your facts list.
• Check how many minutes you used.

Change one thing, then test again. Passing proves only the calls you tried. Grow its job after reviewing real calls.

This made-up example shows the parts together. It is not a customer result.

Sam paints houses alone and can't answer with a brush in hand. Sam's job for the agent: "Answer calls I miss on weekdays, answer basic questions, take a message, and send me anyone with a job in progress."

Sam's facts list says:

• Hours: weekdays, 8 to 5.
• Work: inside and outside painting for homes. No business buildings.
• Area: three named towns.
• How to start: Sam visits to see the job, then sends a written quote.
• Prices: none on the list. The agent says Sam gives a price after the visit.

Sam's rules add two lines. If the caller has a job in progress with Sam, transfer the call. If Sam doesn't answer, take a message, text it to Sam, and promise a call back by the end of the next workday.

A caller asks if Sam paints decks. Decks are not on the list. The agent says it is not sure, takes the name and number, and gives the call back promise.

Sam calls back and adds decks to the list. Sam decides.

An agent can follow rules. It cannot stand behind your name the way you do. Keep these for yourself:

• Prices, quotes and discounts that are not on your list.
• Complaints and refunds.
• Anything that changes a promise to a customer.
• Any call where someone may be hurt.
• Decisions about what the agent is allowed to do next.

You decide which facts change and when its job grows. If unsure, take the call yourself.

There are two kinds of cost. The first is setup: your own time, a kit, or a service. The second is the platform's usage bill. It grows with every minute on calls, for as long as the agent runs.

Platforms charge by the minute, but they do not all meter the same thing. Here are two official price pages we read on October 6, 2026. Prices change, so check each page before you choose.

Read the Vapi row with care. That hosting fee is one part of the bill, not the total. The AI model and the voice add to it.

You may see a range like $0.05 to $0.31 a minute quoted for voice AI. That range mixes the Vapi hosting fee with the top of the Retell agent range. It is not one total rate, and it is not a cap. Your own setup can land anywhere. The parts you pick, your phone number and any add-ons decide your real rate.

To keep the usage bill in view:

• Before launch, add up every part of the per-minute price for the setup you chose.
• Multiply by the call minutes you expect each month. Your phone records can show your minutes today.
• Turn on any usage alert or spend limit the platform offers.
• Check minutes used each week, as part of your review.

For context, here is a published price for a done-for-you voice AI service: A voice AI service: $499 setup plus $109 a month (AgentZap Starter, read 2026-10-04). We read that page again on October 6, 2026. The Starter plan includes 150 minutes, then $0.85 for each extra minute. A service sets the agent up for you. With a kit, you do the setup and pay the platform yourself.

Use the steps yourself, or see what the kits cost. Find the Voice Agent Kit with the rest of the kits.

For jobs beyond calls:

• Our guide shows you how to build any AI agent step by step, for jobs beyond the phone.
• If you want us to build one with you and stay accountable for it, see our work on the AI agent for small business.
• Market Loop is a Truline product. Six steps. You make the big calls.

Truline helps independent owners run your business with AI, wherever you are in the world.

Stuck on a step? book a free call with Desmond. It takes 15 minutes.