What you'll have
A phone number that a dentist, salon, plumber or clinic forwards its calls to. The agent greets callers in the business's name, answers questions from a knowledge base (hours, prices, services), and books a slot on the business's calendar. Calls it can't handle get transferred or logged for a callback.
Who pays for it: Small businesses that miss calls while they're busy with customers: trades, clinics, salons, restaurants. You charge a setup fee plus a monthly fee that covers your minutes and your time.
The stack and what it costs
| Tool | Month 1 | Ongoing (per month) | Notes and source |
|---|---|---|---|
| Retell AI Voice agent platform | Free trial credits $0 | Pay as you go, about 500 minutes – | $0.07–$0.31 per minute on the pricing page, so 500 minutes is roughly $35–$155 (our arithmetic) · Pricing page, read 17 October 2026 |
| Phone number Phone number (Retell-managed, US or Canada) | 1 number $2 | 1 number $2 | $2/month per normal number, $5 toll-free (Retell docs) |
| Cal.com Booking calendar | Free account – | Free account – | Price not verified by us |
| Total | $2 | $37–$157/mo Estimate | Sum of the rows. Excludes tax, per-sale fees and anything marked "–" (not verified or usage-based). |
Plan prices are list prices in USD from each tool's pricing page; plan choices for month 1 and ongoing are our estimate for one person doing this part time.
Step by step
6 of 7 steps are checked against official docs, 1 is our advice. Menu names are quoted from the linked docs as of the date shown; apps change, so follow the doc if what you see differs.
Create a Retell account and use the trial credits
New accounts start with $10 in free trial credits, and you don't need a payment method until you buy a phone number.
Source: Retell docs: Build your first phone agent in 15 minutes, read 20 October 2026
Start from the Receptionist template
Choose Single prompt for your first version. Pick a ready-made template such as Receptionist, build from scratch, or use Generate from prompt to have Retell's assistant draft an agent from a plain-English description.
Source: Retell docs: Build your first phone agent in 15 minutes, read 20 October 2026
Add the business's facts as a knowledge base
Put the greeting, tone and rules in the prompt, and add the FAQ, price list and policies as knowledge-base sources the agent can look up during calls. Retell notes that tables and image-heavy files retrieve less reliably, so add explanatory text.
Source: Retell docs: Knowledge base, read 20 October 2026
Connect Cal.com so it can book
Connect a Cal.com account, then add the Check Availability and Book Appointment tools. Each takes an event type ID (Cal.com now calls event types links): open Links in Cal.com, choose the event, and copy the ID after /links/ in the address.
Source: Retell docs: Cal.com tools, read 20 October 2026
Test in the browser before you pay for anything
Click Test to start a web call, allow microphone access and talk to the agent like a real caller. It's free and needs no phone number. Try awkward questions, wrong dates and background noise.
Source: Retell docs: Build your first phone agent in 15 minutes, read 20 October 2026
Buy a number and assign the agent
Add a payment method, open Phone Numbers in the sidebar, click + to buy a number (optionally by area code), then assign your agent as the inbound agent. Retell-managed numbers are US and Canada only.
Source: Retell docs: Purchase phone number, read 20 October 2026
Forward the line and read every transcript in week one
Have the owner forward missed or after-hours calls to the new number, then fix the prompt wherever callers got stuck. How to forward depends on the business's phone provider.
Our advice. No specific menus involved.
Common mistakes
- Going live without testing silence, accents and people talking over the agent. Billing covers the whole call, including silence (Retell pricing page).
- Quoting a monthly price before you've measured real minutes. Log the per-minute total on test calls.
- Letting the agent guess. Tell it to offer a callback when the knowledge base doesn't cover a question.
- No human handoff. Every client eventually gets a caller who needs a person.
Rights and terms check
Retell is a platform, not a content generator, so output ownership isn't the issue. The law where your client operates is: rules on recording calls and on automated outbound calls vary by country and state, and Retell's docs include a page on do-not-call requests. This isn't legal advice.
A summary of public terms, not legal advice. Commercial-rights matrix
Alternatives and when to pick them
| Tool | When to choose it | Free plan | Price |
|---|---|---|---|
| Vapi | Pick it if you or a developer want more control over models, tools and telephony. Its quickstart gives you a free number to test with; Core is $29/month. | Yes | By usage |
| Synthflow | Pick it if you want a no-code builder and accept less flexibility. | Trial only | Paid plans only |
| Bland AI | Pick it if you mainly need outbound calling at volume. | No | Pay as you go |
Prices for tools without an in-depth profile aren't verified by us; we show the pricing model only.
Still choosing? What's the best voice AI agents tool? · All voice AI agents tools compared
How to get your first customer
- Call local businesses after hours and note who sends you to voicemail. Those are your prospects.
- Build a demo agent for one of them from their own website and send a 60-second recording of a test call.
- Offer a short free pilot on missed calls only, so the risk is low for them.
- Price as setup plus a monthly fee, and put per-minute usage in writing.
Our suggestions, not guarantees. Earnings vary.
FAQ
How much does an AI receptionist cost to run?
On Retell, voice agents are billed per minute ($0.07–$0.31 on its pricing page, read 17 Oct 2026) plus $2 a month for a US or Canadian number. 500 minutes a month works out at roughly $37–$157 including the number. That's our arithmetic from the listed rates, so treat it as an estimate.
Do I need to code?
Not with Retell's dashboard and templates. Vapi is more developer-focused.
Can it book appointments?
Yes. Retell's Cal.com tools check availability and book, reschedule or cancel bookings during the call.
Sources
- Retell docs: Cal.com tools (read 20 October 2026)
- Retell docs: Knowledge base (read 20 October 2026)
- Retell docs: Purchase phone number (read 20 October 2026)
- Retell docs: Build your first phone agent in 15 minutes (read 20 October 2026)
- Retell AI pricing (read 17 October 2026)
Steps checked 20 October 2026; prices checked 17 October 2026. Corrections: hello@agenthustles.com.