AI Agents Accessible APIsVoice agents and telephony

Voice agents and telephony APIs and MCP servers for AI agents

Place and receive phone calls handled by AI voice agents, real-time audio/video rooms.

8 voice agents and telephony APIs an AI agent can call: auth method and header, official MCP server (7), free tier (3), docs links. Machine-readable JSON included. Agents: fetch catalog/voice-agents-telephony.json instead of parsing this page. Last checked 2026-09-24.

Ratings and usage (★) fetched: .

ServiceWhat an agent can doAuthMCP serverFree tierDetails (with sources)NotesProof (ratings, usage)
Bland AIProgrammatically create AI phone agents and place/manage automated outbound and inbound calls.API key
Authorization: Bearer <api_key> header (bare key without prefix still accepted)		officialfree credits + inbound number on signup (Start plan), no credit card requiredBase URL: https://api.bland.ai/v1
Free plan: 2 credits + an inbound number; 100 calls/day, 10 concurrent calls, no card ↗
Rate limits: Start plan: 100 calls/day, 100 calls/hour, 10 concurrent calls; MCP server 120 req/min per org ↗
Async jobs: POST /v1/calls returns call_id; poll call status/logs or pass webhook to receive the call object when it ends ↗
Example call: place an outbound AI phone call: POST https://api.bland.ai/v1/calls ↗
Unit price: Connected calls: $0.14/min on Start (no platform fee), $0.12/min on Build ($299/mo platform fee) ↗
MCP tools: 13: create_call, wait_for_call, stop_call, get_call_log, list_voices, validate_pathway … ↗		MCP server rate-limited to 120 req/min/org; distinguishes read-only vs destructive operations.—
Deepgram Voice Agent APIRun a full-duplex speech-to-speech voice agent pipeline (STT+LLM+TTS) over a WebSocket API.API key
Authorization: Token <api_key>		official$200 free credit on signupFree plan: $200 credit, one-time, no card ↗
Rate limits: Pay As You Go: up to 45 concurrent Voice Agent WSS connections (60 on Growth); STT 150 WSS / 50 REST; TTS 45 ↗
Data policy: Model Improvement Program may keep data for training; opt out per request with mip_opt_out=true (data kept only for processing) ↗
Unit price: Voice Agent Standard: $0.075 per minute of WebSocket connection (Pay As You Go); BYO TTS $0.065/min, BYO LLM $0.059/min, BYO LLM+TTS $0.050/min ↗		Primarily an STT/TTS/voice-agent infra layer, often paired with a telephony provider like Twilio to reach phone calls. MCP server built into the dg CLI ('dg mcp', stdio or SSE); docs MCP at https://developers.deepgram.com/_mcp/server.—
ElevenLabs Agents PlatformBuild and deploy conversational AI voice agents with telephony (SIP/Twilio) integration via API and SDKs.API key
xi-api-key: <api_key>		officialFree plan: 10k credits/month shared across ElevenLabs products; no commercial license (from Starter, $6/month)Base URL: https://api.elevenlabs.io/v1
Free plan: 10k credits, per month ↗
Data policy: Zero Retention Mode available per agent and for Enterprise API use ↗
Example call: create a conversational agent: POST https://api.elevenlabs.io/v1/convai/agents/create ↗
Unit price: Agents (Speech Engine): $0.08 per minute beyond plan-included minutes, $0.16 per burst minute ↗		Official hosted MCP server uses OAuth (sign in with ElevenLabs account) rather than a raw API key; core REST API uses api-key auth.—
LiveKit CloudBuild and deploy real-time voice AI agents with SIP telephony support using LiveKit's server SDKs and APIs.API key
API key + secret sign a JWT access token sent as Authorization: Bearer <token>		—free Build plan: 1,000 agent session minutes/mo, 5,000 WebRTC participant minutes/mo, 50GB data transferFree plan: 1,000 agent session min, 5,000 WebRTC participant min, 50GB transfer, $2.50 inference credits, per month, no card ↗
Rate limits: Build plan: up to 100 concurrent users and agents ↗
Example call: dispatch a voice agent into a room: POST https://{projectDomain}/twirp/livekit.AgentDispatchService/CreateDispatch ↗
Unit price: Agent sessions: $0.01 per minute overage on paid plans (Build includes 1,000 min/mo free); WebRTC overage $0.0004-$0.0005 per participant minute ↗		Self-hosted open-source option also exists; Cloud is the managed offering with usage-based billing beyond the free tier.—
Retell AIBuild, deploy, and manage AI voice agents that handle phone and web calls via REST API and SDKs.API key
Authorization: Bearer <api_key>		official$10 free credit on signup, then pay-as-you-go ($0.07-$0.31/min for voice)Base URL: https://api.retellai.com
Free plan: $10 in free credits, one-time ↗
Rate limits: Pay-As-You-Go workspaces: 20 concurrent calls by default (extra $8/call/month); calls max 1 hour by default ↗
Example call: place an outbound AI phone call: POST https://api.retellai.com/v2/create-phone-call ↗
Unit price: Per call minute: voice infra $0.055 + LLM (e.g. $0.064 GPT 5.6 Terra) + telephony ($0.015 US via Twilio); advertised $0.07-$0.31/min ↗		Official MCP at https://mcp.retellai.com (Streamable HTTP) authenticates with Authorization: Bearer <RETELL_API_KEY>.SourceForge 1.0★/1 review
Synthflow APICreate and manage AI phone voice agents and trigger/manage outbound calls programmatically via REST API.API key
Authorization: Bearer <api_key>		officialPaid only: pricing page lists Enterprise contracts from $30,000/year; no self-serve free trial shownBase URL: https://api.synthflow.ai/v2
Rate limits: Per-workspace concurrency limit and CAPS (calls initiated per second) limit; excess returns 429 or is queued ↗
MCP tools: 17: list_agents, get_agent, create_agent, update_agent, publish_agent_draft, delete_agent … ↗		Go-to-market is enterprise sales. Official remote MCP (~60 tools) also has regional URLs: https://mcp.us.synthflow.ai/mcp and https://mcp.eu.synthflow.ai/mcp.SourceForge 1.0★/1 review
Twilio Programmable VoiceProgrammatically make, receive, and control phone calls (IVR, recording, conferencing) via REST API.API key
Basic Auth (Account SID + Auth Token) or API Key/Secret		officialTrial: one-time free units (e.g. 75 voice minutes, 100 SMS, 100 WhatsApp, 3,000 emails), no card, expires after 30 days; then pay-as-you-goBase URL: https://api.twilio.com/2010-04-01
Free plan: 75 voice minutes, 100 SMS, 100 WhatsApp messages, 3,000 emails; verified numbers only, one-time, no card ↗
Rate limits: Account API concurrency limit; exceeding returns 429 Too Many Requests ↗
Example call: make an outbound call: POST https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/Calls.json ↗
Unit price: US: outbound calls $0.0140/min; inbound $0.0085/min on local numbers (+$1.15/mo per number) ↗		Widely used as the underlying telephony carrier beneath voice-agent platforms (Vapi, Retell, ElevenLabs, LiveKit) for actual call carriage. Twilio's own MCP (npm @twilio-alpha/mcp) is alpha.GitHub 169★ twilio/twilio-oai
GitHub 111★ twilio-labs/mcp
VapiCreate, configure, and run AI voice assistants that make and receive phone calls via REST API.API key
Authorization: Bearer <api_key>		official$5 free credit on signup, then pay-as-you-go (~$0.05/min platform fee + provider costs)Base URL: https://api.vapi.ai
Free plan: $5 free credits, one-time ↗
Rate limits: 4 concurrent calls with no Success Package; 10 on Core ($29/mo), 30 on Pro ↗
Example call: start an outbound phone call with an assistant: POST https://api.vapi.ai/call ↗
Unit price: $0.05 per call minute Vapi hosting fee; transcriber, LLM, voice and telephony billed separately at cost ↗
MCP tools: 10: list_assistants, create_assistant, get_assistant, list_calls, create_call, get_call … ↗		Also has an official MCP server (streamable-HTTP and SSE endpoints) exposing assistants/calls/phone numbers as tools.—

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