Connecting OpenClaw to a Rotary Phone via SIP and Speech APIs
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
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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