Connecting OpenClaw to a Rotary Phone via SIP and Speech APIs

✍️ OpenClawRadar📅 Published: March 8, 2026🔗 Source
Connecting OpenClaw to a Rotary Phone via SIP and Speech APIs
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Hardware and SIP Setup

The setup uses a Benotek rotary phone connected via phone cord to a Grandstream HT801 v2 ATA (Analog Telephone Adapter). The HT801 connects to the router via ethernet and registers as a SIP endpoint with Twilio.

Call Flow: User to OpenClaw

  • Pick up the rotary phone and dial the Twilio number
  • Twilio answers and plays "Connecting you to OpenClaw"
  • Twilio opens a WebSocket media stream to the server via ngrok
  • Server connects to Deepgram for speech-to-text and OpenClaw
  • Voice audio streams from Twilio to Deepgram in real time
  • Deepgram transcribes speech to text
  • After 1.5 seconds of silence, the transcript is sent to OpenClaw
  • OpenClaw responds with text
  • Text is sent to ElevenLabs for text-to-speech conversion
  • Audio is converted to mulaw format via ffmpeg
  • Mulaw audio streams back through Twilio to the rotary phone speaker
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Call Flow: OpenClaw to User

  • Hit the /call-me endpoint on the server
  • Server tells Twilio to call the SIP endpoint (HT801)
  • Rotary phone rings with its mechanical bell
  • Pick up, same flow as above

A demonstration video is available showing the system in action.

📖 Read the full source: r/openclaw

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👀 See Also