The formula
Cost per billed minute = platform fee + AI model + speech-to-text + voice + phone line- Platform fee: the vendor's own per-minute charge, whatever name the vendor gives it.
- AI model: the per-minute charge for the language model, or zero when the vendor says the platform fee includes it.
- Speech-to-text: the charge for turning the caller's speech into text: zero when included, your own figure when the vendor publishes none.
- Voice: the text-to-speech charge, zero when included.
- Phone line: the carrier's per-minute charge, from the vendor or from a carrier you pay directly.
What each vendor's per-minute rate covers
Retell's billing docs say what its $0.055 per minute (Retell Voice Infra) buys: The voice engine; not the AI model or phone. The voice is priced separately, and speech-to-text has no price of its own on the Retell pages this site read (not publicly listed).
Vapi adds its $0.05 per minute hosting fee on top of the other four parts, each billed at the provider's listed price (None: speech, model, voice, transport extra). Its pricing calculator gives a range for speech-to-text, the model and the voice; the model item, for example, shows OpenAI: $0.0077 to $0.0452 per minute (calculator estimate).
ElevenLabs puts more inside its minute. Its plan table lists $0.08 per minute beyond included minutes (Voice and speech-to-text included). The AI model is billed on top by the token, and ElevenLabs says it does not charge extra for telephony, while a provider you connect, such as Twilio or a SIP trunk, bills you directly (Not the AI model; your carrier bills you).
Ultravox draws the line further out. Its $0.05 per minute after 30 free minutes covers the AI model and the voice (Speech understanding and generation included), and its model has no separate speech-to-text step (No separate speech-to-text stage). Its pricing page does not say so; a model announcement and the docs do. The phone line stays outside (Bring your own telephony: SIP trunking, Twilio or other providers), and on Pay As You Go, SIP calls carry a fee of their own (SIP: 0.5¢ per minute).
Bland's pricing page counts the AI model, speech-to-text and the voice inside its $0.14 per minute on the Start plan (In the per-minute rate; no token charges). On the phone line, Bland's pages disagree: The pricing page says telephony is billed separately, while the home page and the docs llms.txt say the per-minute rate covers telephony. No Bland page this site read gives a phone rate (not publicly listed).
Telnyx's $0.05 per minute (voice engine) bundles hosted speech-to-text and hosted voices. On the AI model and the phone line, its pricing page and two machine-readable files on telnyx.com disagree: The Voice AI pricing page bills LLM tokens and telephony on top of the $0.05 voice engine, while telnyx.com/pricing.md and telnyx.com/llms.txt say the $0.05 rate includes SIP and LLM inference.
Synthflow's pricing page says it is sold as an annual enterprise agreement with no rate by the minute (No per-minute rate; annual agreement). Its docs do give a per-minute figure, an overage rate on a Pro plan offered only to Freshworks-connected workspaces, which the pricing page does not mention: $0.13 per minute beyond 2,000 included minutes.
What "platform fee" means depends on whose page you read
On this page, platform fee means a vendor's own per-minute charge, such as Retell's Voice Infra or Vapi's hosting fee; the vendors' pages are less consistent. Retell's pages disagree on what to call its $0.055 per minute (Retell Voice Infra): The pricing page says "No platform fees", while the billing docs call the $0.055 per minute Voice Infra charge, which the same pricing page lists, "the flat per-minute platform cost". On Bland's pricing page the phrase names a monthly charge (Build: $299/month platform fee), paid on top of the Build plan's $0.12 per minute.
Why the real cost comes out above the advertised rate
The first cause is arithmetic: a headline that covers one or two of the five parts leaves the rest for the invoice, and the Retell example below comes to more than twice its voice engine rate. With ElevenLabs or Ultravox the phone line is a second invoice from your own carrier, such as Twilio at its published voice rates.
Model charges also grow with the conversation. Vapi bills the model by the token (Priced per million input and output tokens) and calls its per-minute model figures estimates (Estimates assume 150 output tokens a minute); the same page says long calls often cost more, because the conversation history is sent again. Retell prices models by the minute and stretches the billed time instead (Prompts over 4,000 tokens: billed time grows in proportion).
Some charges run per minute outside the five parts, such as Retell's knowledge base add-on (Knowledge base: +$0.005 per minute). Telnyx's rounding changes how many minutes are billed (Engine: rounded up to the minute, per call).
How the calculator adds up a minute, and what it leaves out
The calculator works on one vendor at a time. Pick a vendor, a plan where there is more than one, and an option for each part the vendor prices; the calculator adds them per billed minute. A part the vendor says is included counts as zero, as does one that does not apply, and what a plan includes can differ from the same vendor's other plans. A part the vendor does not price by the minute, leaves to your own carrier or provider, or leaves unclear on its pages gets a box for your rate; until you fill it in, the total reads as before that part, for example before your phone line, unless the vendor lists no charge for the part, as Retell does for speech-to-text. Where a vendor publishes a range, as Vapi does, the total is a range. Beneath the controls, every vendor it models is listed in order of cost at the choices set for it, with vendors whose figure is complete above a divider and those that still need your own rates below it.
It prices a billed minute only: plan fees, included minutes, rounding, per-call fees and charges for calls at once are left to the calculators on the billed minutes and concurrency limits pages. For some vendors, such as Vapi and ElevenLabs, the model figure is the vendor's own per-minute estimate of a token charge (Passed through at provider rates, no markup), which a long prompt can push higher. Telnyx's model charge is a box for your own estimate: Not priced per minute (billed per token). Under each vendor's total the calculator lists what that figure leaves out. Below the list it names the vendors that publish no per-minute price, such as Synthflow, and, in a separate list when there are any, vendors whose published rates it has not yet added.
A worked example: choose Retell, whose rates here are its Pay as you go rates, and keep the calculator's default for each part. Platform fee: $0.055 per minute (Retell Voice Infra). AI model: $0.032 per minute, GPT 6.1 Terra, the model Retell marks as recommended. Speech-to-text: Not publicly listed, with no statement that it is included, so it counts as zero until you enter a rate. Voice: $0.015 per minute, Retell Platform Voices. Phone line, US: $0.015 per minute (Retell Twilio number). The four priced parts add up to $0.117 per billed minute, which the calculator labels "every part counted".
Often confused with
- Billed minutes. Cost per minute is a rate; billed minutes are what it is multiplied by, after each vendor rounds the call and applies any minimum.
- Cost per call. The rate times a call's billed minutes, plus any fee charged for each call or dial attempt.
- Plan fee. A fixed monthly charge paid on top of per-minute usage, such as Vapi's (Core: $29 per month).
- Concurrency charge. A price for each extra call that can run at the same time, such as Vapi's $10 per extra call line per month, charged however many minutes you use.
Vendors cited on this page
Bland AI, ElevenLabs Agents (ElevenAgents), Retell AI, Synthflow AI, Telnyx Voice AI Agents, Ultravox, Vapi. Each profile lists everything that vendor publishes, with its sources. All of them are side by side in the comparison.
Sources
- Twilio, Programmable Voice pricing, United States read 14 Nov 2026
Checked against its sources on 14 Nov 2026. Vendor figures on this page open their source when clicked. Lexicost has no commercial relationship with any vendor named on this site.