A voice agent platform runs the loop. A caller speaks, the audio is transcribed, a language model decides what to say, the reply is synthesised, and the audio goes back down a phone line. That cycle repeats every few hundred milliseconds until somebody hangs up.
The platform is the thing holding that loop together. It is not the thing doing any of the four steps.
The four components
- Speech recognition turns the caller's audio into text. Deepgram, AssemblyAI and Whisper live here.
- The language model decides the reply. Any of the general providers, and the one place the platform usually lets you choose.
- Speech synthesis turns text back into audio. ElevenLabs, Cartesia, Rime. This is the component with the widest price range by a distance.
- Telephony carries the call. Twilio, Telnyx, SignalWire, Plivo. A pure pass-through, and the easiest line to cut.
You can buy all four directly. This site computes what that costs from four dated published rates: $0.0465 a minute. That figure is the test.
What the platform adds
Turn-taking, mostly, and it is harder than it sounds. Knowing when the caller has finished speaking rather than merely paused, handling the case where they talk over the agent, and keeping the whole round trip fast enough that the silence does not feel wrong.
Then the operational layer: a phone number, call recording, transcripts, a way to define what the agent may do, tool calls into your own systems, and a transfer path to a human. Assembled yourself, that is a project. Bought, it is a line item.
How to tell which one you are looking at
Compare the advertised rate to $0.0465 and ask what is missing.
A product advertising well below the floor is selling you one layer. Voximplant at $0.004 and LiveKit Agents at $0.01 are transport: real rates, small slices. A product advertising near or above it is either bundling components it makes itself, or passing them through at cost and charging for the orchestration.
The rate tells you where the boundary is drawn. That is the most useful single thing to know about this category, and it is why a ranked list of per-minute prices is close to meaningless without an exclusion column beside it.
Only 12 of the 34 platforms here publish a rate at all, and 13 have no self-serve path. So for roughly two thirds of the category the boundary question cannot be answered from the outside, and the first thing to ask on a sales call is not what it costs but which of the four components that price includes.
When you do not need one
Three cases. If the call is entirely outbound and entirely scripted, a dialler is a better fit and cheaper. If the interaction has no phone in it, you want a chat product, and several tools sold as voice agents are chatbots with a telephony adapter.
And if you have engineers who will own this, going direct is materially cheaper and gets materially more predictable. The orchestration is a week of work and then a standing maintenance job. That trade is worth making at high volume and almost never worth making below a few thousand minutes a month.