A web service exposes /health; a phone line exposes nothing. The telephone is the oldest telecommunication tool still in production — and our LLM voice agents answer customer calls over it, with no way to know whether they are answering, hearing, and behaving correctly right now.
So we gave a frontier model a telephone.
Our MCP server gives any LLM a phone: dial PSTN numbers, speak via TTS, and read the other side via silence-detected transcripts. A frontier model becomes the caller, phoning our production voice agents in an agent-calls-agent loop — one mechanism covering the whole testing spectrum: ping-style health checks, deep evaluation via scripted and adversarial conversations, and load testing with concurrent caller fleets.
We cover the MCP tool design for a domain the spec wasn't written for — tools that block for tens of seconds, turn-taking over live audio, per-call session state — where the spec fought us and what we would feed back, plus what broke: timeout cascades and evaluations that flap.
We are open-sourcing the server. You'll leave knowing how to connect your own agent to the PSTN — and how to ping, probe, and load-test anything that answers a phone.
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Presentation Language: Japanese
Captioning will be available for attendees in 50+ languages through Wordly. See instructions in each room to utilize captioning.
