AgentPhone | Phone Numbers for AI Agents

# Agent Phone > Phone numbers for AI agents. Give your AI a real phone number. Agent Phone is an API platform that gives AI agents phone identities. Developers use Agent Phone to provision real US/Canadian phone numbers and connect them to AI agents for SMS and voice communication. ## Key Features - **Instant Phone Numbers**: Provision US and Canadian phone numbers via API in seconds - **Two Voice Modes**: Built-in AI (zero infrastructure) or Custom Webhook (full control) - **Unified Webhook**: One `agent.message` event for both SMS and voice, with full conversation history - **Per-Agent Webhooks**: Route events to different endpoints per agent (overrides the project default) - **Stateful Conversations**: Messages and calls auto-thread into durable conversation history with custom metadata - **Voice Abstraction**: Simple JSON transcript-to-response loop — no TwiML or WebSocket management - **Production-Grade**: HMAC+timestamp signatures, idempotency headers, exponential backoff retries - **MCP Server**: Model Context Protocol support for tool-using AI agents (Cursor, Claude Code, Windsurf) ## Voice Modes Every agent has a `voiceMode` that controls how voice calls are handled: ### Built-in AI (`"hosted"`) - Calls are handled end-to-end by an AI using your system prompt - No server or webhook needed — works immediately - Provide `systemPrompt` (required), `beginMessage` (optional greeting), and `voice` (TTS voice ID) - Best for: quick prototyping, simple conversational agents ### Custom Webhook (`"webhook"`) - Caller speech is transcribed and sent to your webhook as `agent.message` events - Your server controls every response — use any LLM, RAG, or custom logic - Requires a webhook endpoint configured for your project or agent - Best for: production agents that need tool use, database access, or custom business logic ### Switching Modes Switch at any time via `PATCH /v1/agents/:id` with `{"voiceMode": "hosted", "systemPrompt": "..."}` or `{"voiceMode":

{ "openapi": "3.1.0", "info": { "title": "AgentPhone API", "description": "API for managing AI phone agents, phone numbers, conversations, calls, and webhooks", "version": "1.0.0" }, "paths": { "/v0/agent/sign-up": { "post": { "tags": [ "agent-signup" ], "summary": "Agent Sign Up", "description": "Kick off agent self-signup.\n\nSends a 6-digit OTP to the human's email. Nothing is provisioned server-side\nuntil /v0/agent/veri