A Phone Number That Interprets Calls in 47 Languages — and the Hard Parts of Building It

kolchinski · reddit · 2026-09-03

ThunderPhone launched a free phone interpreting service: call (228) 888-8666 to merge bidirectional interpretation into a call, or use speakerphone for in-person talks — no app or account needed. Built from a 2024 hackathon project and rebuilt on the team's production voice-AI platform, it surfaces three hard lessons:

Turn-taking is harder than translation: a pause isn't always the end of an utterance, and pauses vary by language. They run VAD per speaker and tune end-of-turn detection per language.
Phone audio loses a lot: 8 kHz narrowband plus compression, noise, and crosstalk. They run multiple transcription models in parallel and fuse outputs, while also piping audio directly into LLMs — either path can be wrong, both together help.
Everything streams: calls come in over SIP through a streaming pipeline of transcription, translation, and speech. Some latency remains and heavy crosstalk still trips it, but it feels close to a real interpreted call.

47 languages fully supported; around 70 usually work, with quality dropping on long-tail languages.

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A Phone Number That Interprets Calls in 47 Languages — and the Hard Parts of Building It

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