Synthflow, Rosie, Goodcall and Smith.ai all promise to answer the phone when you can't. They bill in four different units — minutes, unique callers, calls, and stacked per-minute components — so the headline price tells you almost nothing. This guide converts each model into the same call patterns, and checks the other question that matters: when a call needs a human, who picks up?
Professional: 250 minutes included. Booking and live transfers start on Scale, $149/mo.
Starter: 100 unique customers included. Minutes are never metered.
AI Receptionist: free for 25 calls/mo. Pro is $150/mo for 75 calls, billed per call.
Currently sold as an enterprise agreement scoped with sales. Usage components reported at roughly $0.11–$0.16/min — see the pricing note below.
| Rosie AI | Goodcall | Smith.ai (AI Receptionist) | Synthflow | |
|---|---|---|---|---|
| Best for | Solo owners and small shops that miss calls after hours | Businesses with repeat callers and unpredictable call lengths | Law firms and intake-heavy services; anyone who wants human backup | Agencies and teams that want to design their own voice agents |
| How it bills | Monthly minute bundles | Per unique caller per month (minutes unmetered) | Per call (call length does not change the price) | Enterprise agreement; usage is component-based per minute where pay-as-you-go applies |
| Published prices | $49 (250 min) / $149 (1,000 min) / $299 (2,000 min) | $79 (100 customers) / $129 (500) / $299 (2,000) | Free (25 calls) / $150 (75 calls) / $270 (150) / $500 (300) | Custom. Third-party trackers citing the vendor's pricing put components at ~$0.11–$0.16/min plus $1.50/mo per number |
| Overage | No published per-minute overage rate — confirm what happens over your bundle before signing up | Per extra unique customer: 79¢ / 26¢ / 15¢ by plan | Per extra call: $3.00 on Free, $2.50 down to $2.10 by tier | Per-minute usage; extras such as added concurrency are charged separately |
| Free option | 7-day free trial (no free-forever plan) | Free demo agent; billing starts when you connect a number | Free plan with 25 calls/month | None published under the current enterprise model |
| Human escalation | Transfers to your own staff (Scale and up: warm and live transfers; Growth: waterfall across numbers). No vendor human network | Transfers to escalation contacts you configure — up to three contacts tried in sequence. No vendor human network | Live Agent Handoff to Smith.ai's own North America-based receptionists (paid add-on on AI plans, included on Enterprise), plus separate fully-human plans | Transfers are something you build into the flow. No vendor human network |
| Booking | Direct calendar booking on Scale and up; entry plan sends a booking link by text | Books on Google Calendar; native links to Sheets and HighLevel, Zapier for the rest | Scheduling and intake with native legal / CRM integrations and Zapier | Via integrations and API actions you configure (calendar, CRM, webhooks) |
| Languages | English and Spanish | English (some vendor pages also list Spanish — the vendor's own pages are not consistent; no Japanese) | English and Spanish, including bilingual human agents | 30+ languages listed, including Japanese |
| Phone numbers | US numbers (pick your area code) | Local US numbers only — no toll-free, Canadian or international numbers yet (vendor FAQ) | US-focused; human agents are North America-based | Numbers sold in-platform for US, Canada and Australia only; other countries require bringing your own carrier / Twilio number |
| Trade-off to know | The $49 plan takes messages but does not book or transfer — the service most people picture starts at $149 | Charged per agent, and a wave of brand-new callers eats the allowance fast | Highest per-unit price of the three self-serve options here; you pay for the intake workflow and the human safety net | Pricing has changed repeatedly and is now quote-based — the hardest of the four to budget from public information |
Prices are USD, before tax, as published by the vendors in November 2026. Synthflow is the exception to handle with care: its own recent pages describe an annual enterprise agreement with no published per-minute rate, while 2026 trackers that read its pricing page earlier report pay-as-you-go components (voice engine $0.09/min + LLM $0.02–$0.05/min + telephony $0.00–$0.02/min). We show both because sources disagree; confirm the current model with sales before budgeting. Plans change — always confirm the current price and what's included on the vendor's site before you buy.
Headline prices can't be compared across four different billing units, so we ran the same call patterns through each vendor's published pricing. These are arithmetic on list prices — not test results.
| Scenario | Rosie | Goodcall | Smith.ai AI | Synthflow (usage only) |
|---|---|---|---|---|
| A: 100 calls/mo, avg 3 min (300 min, 80 unique callers) | $149 — 300 min exceeds the 250-min plan, so Scale (1,000 min). $1.49/call | $79 — 80 unique callers fit Starter. $0.79/call | $212.50 — Pro 75 calls ($150) + 25 extra calls × $2.50. $2.13/call | $34.50–$49.50 — 300 min × $0.11–$0.16 + $1.50 number. Usage math only; current sales model is a custom agreement, so this may not be a price you can actually buy |
| B: 100 calls/mo, avg 6 min (600 min, 80 unique callers) | $149 — still inside Scale's 1,000 min | $79 — unchanged; minutes are never counted | $212.50 — unchanged; per-call pricing ignores duration | $67.50–$97.50 — usage doubles with minutes |
| C: 25 calls/mo, avg 3 min (75 min, 20 unique callers) | $49 — Professional covers 250 min | $79 — Starter is the floor plan | $0 — exactly the free plan's 25 calls (call 26 is $3.00) | $9.75–$13.50 — usage only, same caveat as above |
Three patterns worth noticing. First, the cheapest option changes with the scenario — there is no single winner. Second, doubling average call length (A → B) moves only the minute-based bills; per-call and per-caller pricing don't react to talkative callers at all. Third, compare all of this with a human answering service: Smith.ai's own human Virtual Receptionist plans run $300/mo for 30 calls, $810 for 90 and $2,100 for 300 — roughly five to six times its AI per-call rates for the same company. That gap buys a person who can handle nuance, complaints and exceptions, which is exactly why the handoff design in the next sections matters more than the last dollar.
Rosie is a ready-made AI answering service for small businesses: it trains on your website and Google Business Profile, answers 24/7, takes messages, and sends a summary, transcript and recording after each call. Pricing is a simple minute ladder — Professional $49/mo (250 minutes), Scale $149/mo (1,000 minutes), Growth $299/mo (2,000 minutes) — with a 7-day free trial and two months free on annual billing. Every plan speaks English and Spanish and handles several calls at once. The catch is in the plan split: the $49 tier takes messages and texts callers a booking link, but direct calendar booking, warm transfers (Rosie briefs your team before connecting) and live transfers start at Scale. Rosie is AI-only — escalation means transferring to your own people, and there is no published per-minute overage rate, so ask what happens in a busy month before you rely on the entry plan.
Goodcall's difference is its billing unit: it counts unique customers — one phone number, once a month — and never meters minutes, calls or tokens. Starter is $79/mo for 100 unique customers, Growth $129 for 500, Scale $299 for 2,000, each including a local US number, month-to-month with no setup fee; extra customers cost 79¢, 26¢ or 15¢ depending on the plan, and spam and wrong numbers don't count. The agent answers FAQs from your business information, qualifies leads, books on Google Calendar and sends you the details by text and email. When it can't help, it transfers to escalation contacts you configure, trying up to three in sequence. The model shines when the same customers call repeatedly or calls run long. It is less kind to campaigns that generate many one-time callers, pricing is per agent, and — per the vendor's own FAQ — numbers are local US only, with no toll-free or international numbers yet.
Smith.ai sells two things under one roof: an AI Receptionist billed per call, and a Virtual Receptionist service staffed by 500+ North America-based human agents — and the AI plans can hand off to those humans. AI pricing is published in full: a free plan with 25 calls/month ($3.00 per extra call), then Pro at $150/mo for 75 calls ($2.00/call), $270 for 150 and $500 for 300, with per-call rates improving to $1.67 at volume; spam calls are filtered before billing. Because billing is per call, a careful 20-minute intake costs the same as a 2-minute screen — the model law firms and other intake-heavy businesses are built around, with native integrations for legal and CRM tools. The hybrid design is the real differentiator: Live Agent Handoff is available as a paid add-on on AI plans (and included on Enterprise), so a complex or sensitive caller can reach a person instead of a dead end, and full human plans start at $300/mo for 30 calls if you want people from the first ring. Coverage is English and Spanish.
Synthflow is a no-code platform for designing your own voice agents — inbound receptionists, outbound callers, lead qualification, appointment booking — using a visual flow builder, knowledge bases and integrations with CRMs, calendars and APIs. That flexibility is the product: you decide what the agent asks, when it transfers, and what it writes back to your systems. The trade-off is that you also own the design work, and pricing is the least settled of the four. Synthflow's own recent pages describe it as an annual enterprise agreement, scoped to call volume, telephony, integrations and security needs, with no free plan and no published per-minute rate; 2026 trackers that read its pricing page report pay-as-you-go components of roughly $0.11–$0.16 per minute (voice engine $0.09 + LLM $0.02–$0.05 + telephony $0.00–$0.02), phone numbers at $1.50/month and five concurrent calls included. Treat the per-minute figures as a modelling input, not a quote. Synthflow lists 30+ languages including Japanese — the broadest language list here — but sells numbers in-platform only for the US, Canada and Australia; a number anywhere else means bringing your own carrier arrangement.
You need three numbers: how many calls, the average length, and how many different people called. Those three figures — not the headline price — decide which billing model is cheapest for you, as the scenarios above show.
Short, simple questions → minute bundles (Rosie) or usage pricing. Long intakes → per-call (Smith.ai). The same loyal customers calling again and again → per-unique-caller (Goodcall). Custom flows across systems → Synthflow.
Check four things: Does a person ever pick up — the vendor's agents, or only your staff? Is the transfer warm (context passed) or cold? Who is the fallback at 2 a.m., when your staff are the ones asleep? And does a handoff cost extra? If nobody can answer those, the honest design is AI + a good message-and-callback routine.
Use Rosie's 7-day trial, Smith.ai's free 25 calls, or Goodcall's free demo agent, and forward real after-hours calls to it. Check the summary against what the caller actually wanted. And confirm the basics in writing: your country's numbers, your callers' language, and what happens when you exceed your plan.
None of them, in general. In our worked scenarios, Goodcall's per-caller pricing was cheapest at 100 calls ($79), Smith.ai's free tier was cheapest at 25 calls ($0), and minute-based pricing wins when calls are short and few. The billing unit that matches your call pattern is the cheap one — which is why Step 1 is pulling your own call log.
For defined, repeatable work — hours, directions, booking, lead details, message-taking — published feature sets cover it, and the price gap is large (AI plans here run $49–$299/mo; human services run from $300/mo for just 30 calls). For complaints, negotiations and sensitive matters, a person is still the safer receiver. The middle design, and the one we would check first, is hybrid: AI answers first, humans take over when the call needs one.
It depends on the service, and this is the most important difference in this comparison. Smith.ai can hand off to its own live agents (add-on on AI plans, included on Enterprise). Rosie and Goodcall transfer to people on your side — Rosie with warm and waterfall transfers on higher tiers, Goodcall to up to three escalation contacts in sequence. Synthflow transfers wherever your flow sends it. Every service can fall back to taking a message with a summary and transcript.
Mostly, no — and we flag this plainly because it decides the purchase for many readers. Goodcall's own FAQ says its numbers are local US numbers only. Rosie and Smith.ai answer in English and Spanish. Synthflow is the partial exception: Japanese is in its published language list, but it sells numbers directly only for the US, Canada and Australia, so a Japanese number means bringing your own carrier setup. If your callers are in Japan, a domestic Japanese answering service is the realistic comparison — this guide's four services are built for the US market.
Because this guide is compiled from the vendors' published specifications and pricing, not from hands-on testing we haven't done. Judgments that do appear — for example, which billing model suits long calls — are arithmetic on the published prices, shown in the scenario table so you can check them yourself.