Guide · AI Receptionists
Four voice-AI platforms charge no monthly base and bundle zero minutes — so you can pay for a single test call
Synthflow, Vapi, Retell and Bland are the pure pay-as-you-go options here: $0/mo, no included minutes, billed per minute from the first second. Their headline rates span 2.8x — and cover different slices of the call.
Six vendors in our dataset publish a $0/mo entry plan, but only four of them mean “no commitment” the way a usage-only buyer does: no monthly base, nothing bundled, and a meter that starts on the first connected minute. Those four are Vapi (Build), Retell AI (Pay As You Go), Synthflow (Pay As You Go), and Bland (Start) — every one carries a $0/mo platform fee, lists minutesIncluded as null, and bills purely per minute. The other two $0/mo plans, Phonely Free (100 bundled minutes) and My AI Front Desk Free (20 bundled minutes), are also commitment-free, but they hand you a fixed minute allowance rather than open-ended pay-per-use — a different offer, covered separately. If your literal requirement is “open an account, run one test call, pay for exactly that one call,” the four pure pay-as-you-go platforms are the set, because none of them includes a single bundled minute for you to leave unused.
What “what you use” costs is where they split. The marginal rate runs from $0.05/min on Vapi to $0.14/min on Bland — a 2.8x spread on the headline number alone (0.14 ÷ 0.05 = 2.8). But the bigger trap is that the four rates don’t describe the same thing.
The four zero-commitment rates, and what each one covers
| Vendor | Plan | Platform fee | Per-minute rate | What the rate includes |
|---|---|---|---|---|
| Vapi | Build (PAYG) | $0/mo | $0.05/min | Platform fee only — LLM/STT/TTS passed through at cost |
| Retell AI | Pay As You Go | $0/mo | $0.055/min floor | Voice infra only — LLM + telephony ($0.015/min) on top |
| Synthflow | Pay As You Go | $0/mo | $0.09/min | Voice Engine only — LLM ($0.02–$0.05/min) + telephony additive |
| Bland | Start | $0/mo | $0.14/min | All-in — LLM + STT + TTS + telephony |
Read the right-hand column before the price column. Vapi’s $0.05/min is a platform fee with the language model, speech-to-text, and text-to-speech billed through “at cost” on top — so $0.05 is a floor you will never actually pay in production. Retell’s stored rate is a $0.055/min infra floor; the vendor’s own published all-in range is $0.07–$0.31/min once you add an LLM and US telephony at $0.015/min. Synthflow’s $0.09 is the Voice Engine alone, with the LLM at $0.02–$0.05/min and telephony billed separately.
Among these four, Bland’s Start plan is the only one whose per-minute rate is explicitly all-in — model, speech, and telephony included — which is exactly why it sits highest at $0.14/min. The cheapest-looking number in this group and the most honest number in this group are not the same row.
The “single test call” math makes the point concrete. Run one 3-minute test and the bill is the rate times three: $0.15 on Vapi’s platform fee, $0.27 on Synthflow’s engine, $0.42 on Bland’s all-in $0.14 — but only Bland’s $0.42 is a finished number. Vapi’s $0.15 and Synthflow’s $0.27 still owe you a model and telephony bill that the pricing page doesn’t total for you.
So which is actually the cheapest pay-as-you-go?
It depends entirely on whether you want to assemble a model stack. If you are a developer who will wire up your own LLM and telephony, Vapi’s $0.05 and Retell’s $0.055 are genuinely low platform taxes and the real bill lands somewhere in Retell’s published $0.07–$0.31/min band depending on the models you pick. If you want a single rate you can multiply by your call minutes and trust, Bland’s $0.14/min all-in is the figure you can take at face value — higher sticker, fewer surprises. (Which of these is cheapest per real minute once the stack is assembled is a separate question; here the point is narrower — which ones cost you nothing to open and nothing to leave idle.)
Synthflow sits awkwardly in the middle: a $0.09 Voice Engine rate that still needs LLM and telephony stacked on top, plus reseller and concurrency add-ons ($2,000/mo white-label, $20/unit/mo extra concurrency) that signal it is built for agencies more than for a single business testing the water.
The compliance footnote that reorders the list
For a healthcare buyer the ranking changes before price does. Among these four, three — Vapi, Retell AI, and Bland — publish HIPAA support with an available signed BAA. Synthflow does not: its HIPAA is called out for Enterprise only and no BAA is published, so the one mid-priced option in this set drops out of a compliant shortlist entirely.
And the cheapest-looking name carries the catch here too: Vapi’s BAA is a $2,000/mo add-on. The platform that starts at $0/mo and $0.05/min becomes a $2,000/mo line item the moment you need HIPAA — which inverts the entire “no monthly commitment” premise for any clinic. Among these four, for a regulated buyer who genuinely wants zero commitment, Retell (BAA available, $0.055/min infra floor) and Bland (BAA available, $0.14/min all-in) are the two that keep the promise without a four-figure compliance gate.
How to read this
Four platforms in this dataset let you start at $0/mo with nothing bundled and pay per minute: Vapi, Retell, Synthflow, and Bland. (Two more $0/mo plans — Phonely’s 100 minutes and My AI Front Desk’s 20 — are commitment-free too, but they bundle a fixed allowance instead of billing pure usage.) The honest one-line answer is that “free to start” is real and the per-minute economics are not interchangeable — $0.05 buys you a platform fee, $0.14 buys you a finished call, and the 2.8x gap between them is almost entirely the difference between a rate you’ll assemble around and a rate you’ll actually pay. Decide whether you’re buying a building block or a working receptionist first; the cheapest column answers a different question than the one most buyers are asking.