The question is fair and it gets asked constantly. Vapi publishes $0.05 a minute. Slang.ai publishes $399 a month. Both answer a phone and book an appointment. Where does the difference go?
The break-even, computed
This site computes a component floor of $0.0465 a minute from four dated published rates: speech recognition, the language model, speech synthesis, and telephony. That is what the raw minutes cost before anybody adds software or margin.
Divide each vertical vendor's monthly price by that floor and you get the volume at which the subscription equals the cost of the minutes it is buying.
| Vertical tool | Monthly | Break-even minutes | At 4-minute calls |
|---|---|---|---|
| Rosie | $49 | 1,054 | ~264 calls |
| Goodcall | $79 | 1,699 | ~425 calls |
| Parakeet | $199 | 4,280 | ~1,070 calls |
| Slang.ai | $399 | 8,581 | ~2,145 calls |
| Sameday AI | $449 | 9,656 | ~2,414 calls |
| Structurely | $598.80 | 12,877 | ~3,219 calls |
Most single-location businesses take somewhere between 200 and 600 calls a month. At 300 four-minute calls, you are using 1,200 minutes, which costs about $56 in components.
So a $399 plan at that volume is roughly $343 a month of something other than minutes. That is the number the question is really asking about, and it is worth being precise about what it buys.
What the $343 is
- The integration. A calendar or practice system write path that somebody built and maintains against an API that changes.
- The prompt work. A voice agent configured for one industry's vocabulary, objections and edge cases, which is weeks of iteration you are not doing.
- The phone number and the telephony account, which on the platform route you set up and own yourself.
- Somebody to call. When the agent books a patient into a slot that does not exist, there is a support queue rather than a Discord.
- The bet on your volume. Flat pricing means the vendor absorbs a busy month. That is worth something, and it is worth less than it sounds if your months do not vary.
None of that is nothing. The question is whether it is $343 a month of value to you specifically, and that depends almost entirely on whether you would otherwise do the integration yourself.
What the platform route actually costs
Not $0.05 a minute. That is the platform's rate, and it sits on top of the components rather than including all of them, which is why the computed floor and the advertised rate are different numbers.
The real platform bill is the per-minute rate, plus whatever the platform excludes, plus a phone number, plus your own time. That last item is the one that decides it. Building a working inbound agent that reliably books into a calendar is a week of somebody competent, and then it is a standing maintenance job forever.
At a loaded internal rate, one week of engineering costs more than a year of Slang.ai. If nobody on your team is going to own it, the vertical tool is cheaper on any honest accounting, and the $343 stops looking like margin.
When the platform genuinely wins
Three cases, and they are narrower than the platform vendors imply.
High volume. Above the break-even the arithmetic inverts and keeps inverting. A business running 20,000 minutes a month is paying a vertical vendor several times the component cost, and at that scale the engineering is cheap by comparison.
Many identical deployments. An agency running the same agent for forty clients builds once and amortises. That is a different business from a practice buying one phone line, and it is the case the white-label market exists for.
A requirement nobody sells. If the thing you need the agent to do is not what any vertical vendor built, no amount of configuration gets you there and the platform is the only route.