Voice AI’s real call cost is more than minutes: STT, TTS, SIP and retries
decant338 · reddit · 2026-07-27
The author says the headline per-minute price of Voice AI products hides the real cost of a phone call. A typical STT → LLM → TTS pipeline also has platform fees, transcription, model usage, voice generation, SIP/PSTN charges, recording, failed calls, and phone-number rental. Realtime speech-to-speech systems add another wrinkle because input and output audio can be priced separately, and carrier rates vary by destination country.
To make the math easier, the author built an open-source Astro project that includes:
- cost calculators
- country-specific SIP estimates
- latency data
- Asterisk configuration examples
- a local call-log diagnostic tool
They say the formulas and sources are public and explicitly invite corrections from people running Voice AI in production.
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