MCP, A2A and a real phone line in one interface

1 Connect your own agent

Already run an agent? Keep it. connect_agent points a business at your agent's HTTPS receiver. New inbound text conversations then reach your agent as signed events with retries. With a2a_enabled: true, public A2A message/send goes to the same receiver, or to an A2A endpoint you already run via a2a_url.

{
  "name": "connect_agent",
  "arguments": {
    "agent_id": "YOUR_KAI_AGENT_ID",
    "external_agent_id": "my-agent",
    "webhook_url": "https://your-agent.example.com/callmcp/events",
    "idempotency_key": "connect-my-agent-1",
    "a2a_enabled": true
    // optional: "a2a_url": "https://your-agent.example.com/a2a"
  }
}
// needs scopes agents:write, sms:write, webhooks:write
// the signing secret comes back once: store it

In your receiver, the KaiCalls SDK helper handleA2ARequest (TypeScript) or handle_a2a_request (Python) checks the signature and freshness, then hands the text to your agent. Phone audio is not routed to an external agent: the built-in voice runtime answers calls. Connecting grants no extra permissions and does not turn on a channel that isn't registered.

2 Message a business over A2A Beta

Any A2A client can send a public inquiry to a business on KaiCalls. GET on the same URL returns that business's own agent card.

POST https://www.kaicalls.com/api/a2a?handle=BUSINESS_ID_OR_PHONE
Content-Type: application/json

{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "message/send",
  "params": {
    "message": {
      "role": "user",
      "messageId": "msg-1",
      "parts": [{ "kind": "text", "text": "Can we book a service visit Tuesday?" }]
    }
  }
}
// reply: a message with a contextId. Send it back to continue.