# Phone calling and voice transport APIs for agents

> 10 phone calling & voice transport listings ranked by the Anchor benchmark. Leader Twilio Programmable Voice API + MCP (A). The calling layer an agent connects to. Numbers, inbound and outbound calls, audio streaming over websockets or SIP, transfers and recordings. Compared on setup, webhook reliability, where numbers are available and the full cost of a call.

- Canonical: https://www.anchorterminal.com/categories/voice-calling
- Markdown: https://www.anchorterminal.com/categories/voice-calling.md (~2,950 tokens)
- Slim: https://www.anchorterminal.com/categories/voice-calling.min.md (~580 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/categories/voice-calling.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-05

The calling layer an agent connects to. Numbers, inbound and outbound calls, audio streaming over websockets or SIP, transfers and recordings. Compared on setup, webhook reliability, where numbers are available and the full cost of a call.

- Tools ranked: 10 · agent-ready (BB or better): 2 · accept x402: 1 · hosted endpoints: 9 · desk reviews by the panel: 32
- JSON: https://www.anchorterminal.com/api/v1/tools.json (list) · https://www.anchorterminal.com/api/v1/rankings.json (ranked) · https://www.anchorterminal.com/api/v1/x402.json (payable) · https://www.anchorterminal.com/api/v1/capabilities.json (by capability)
- Grades run AA, A, BB, B, C, D, E, F · methodology: https://www.anchorterminal.com/benchmark/

- Capabilities in this category: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording
- https://letme.dev/voice.calls picks the top-graded tool in this list and says how to call it direct; calling through letme comes later (https://www.anchorterminal.com/letme/index.md)

## Ranking

| # | Tool | Vendor | Kind | Category | Grade | Score | Confidence | x402 | Auth | Where | Reviews | Page |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 6 | Twilio Programmable Voice API + MCP | Twilio | HTTP API | Calling | A | 80.4 | medium | no | OAuth or key | hosted + local | 3.1/5 (8) | https://www.anchorterminal.com/tools/twilio-voice.md |
| 48 | Telnyx Voice API + MCP | Telnyx | HTTP API | Calling | BB | 74.4 | medium | payer | OAuth or key | hosted + local | 3.5/5 (8) | https://www.anchorterminal.com/tools/telnyx-voice.md |
| 144 | SignalWire Voice API | SignalWire | HTTP API | Calling | B | 67.3 | medium | no | API key | local | 3.5/5 (2) | https://www.anchorterminal.com/tools/signalwire-voice.md |
| 196 | Bandwidth Voice API + MCP | Bandwidth | HTTP API | Calling | B | 63.7 | medium | no | OAuth | hosted + local | 3/5 (2) | https://www.anchorterminal.com/tools/bandwidth-voice.md |
| 212 | Sinch Voice API + MCP | Sinch | HTTP API | Calling | B | 62.8 | medium | no | OAuth or key | hosted + local | 3/5 (2) | https://www.anchorterminal.com/tools/sinch-voice.md |
| 246 | Infobip Calls API + MCP | Infobip | HTTP API | Calling | C | 60.5 | medium | no | OAuth or key | hosted | 2/5 (2) | https://www.anchorterminal.com/tools/infobip-calls.md |
| 248 | Plivo Voice API | Plivo | HTTP API | Calling | C | 60.4 | medium | no | API key | hosted | 3.5/5 (2) | https://www.anchorterminal.com/tools/plivo-voice.md |
| 270 | Vonage Voice API + MCP | Vonage (Ericsson) | HTTP API | Calling | C | 59.1 | low | no | OAuth or key | hosted + local | 2.5/5 (2) | https://www.anchorterminal.com/tools/vonage-voice.md |
| 346 | Voximplant | Voximplant | HTTP API | Calling | D | 51.9 | medium | no | OAuth or key | hosted | 3/5 (2) | https://www.anchorterminal.com/tools/voximplant.md |
| 424 | Exotel Voice API + MCP | Exotel | HTTP API | Calling | E | 39.8 | medium | no | API key | hosted | 2/5 (2) | https://www.anchorterminal.com/tools/exotel-voice.md |

Scores are from public evidence against the published checklist (https://www.anchorterminal.com/benchmark/), with Performance and Task success pending. p95 latency and context cost come from our probes, which haven't run yet.

## Summaries

### 6. Twilio Programmable Voice API + MCP, A (80.4)

Programmable Voice for placing and answering calls on Twilio numbers in 100+ countries, controlled with TwiML or REST. Twilio APIs SLA at 99.95 per cent for every paying customer, with 10 per cent credits. US outbound at $0.014 a minute, plus $0.0044 for Media Streams or $0.07 for ConversationRelay.

- Page: https://www.anchorterminal.com/tools/twilio-voice · Markdown: https://www.anchorterminal.com/tools/twilio-voice.md · JSON: https://www.anchorterminal.com/api/v1/tools/twilio-voice.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer · endpoint: `https://api.twilio.com/2010-04-01`

### 48. Telnyx Voice API + MCP, BB (74.4)

Carrier-owned Voice API (Call Control and TeXML) for calls, numbers, websocket media streaming, recording and transfers on Telnyx's own network. About $0.007 a minute all-in for US outbound ($0.002 Voice API plus $0.005 termination). x402 and MPP only top up credit, they don't pay per call.

- Page: https://www.anchorterminal.com/tools/telnyx-voice · Markdown: https://www.anchorterminal.com/tools/telnyx-voice.md · JSON: https://www.anchorterminal.com/api/v1/tools/telnyx-voice.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer · endpoint: `https://api.telnyx.com/v2`

### 144. SignalWire Voice API, B (67.3)

Programmable calling API from the team behind FreeSWITCH. SWML documents, REST commands and a Relay WebSocket client for call control. Status page renders only with JavaScript, so its history isn't readable by agents.

- Page: https://www.anchorterminal.com/tools/signalwire-voice · Markdown: https://www.anchorterminal.com/tools/signalwire-voice.md · JSON: https://www.anchorterminal.com/api/v1/tools/signalwire-voice.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer

### 196. Bandwidth Voice API + MCP, B (63.7)

Programmable voice on Bandwidth's own US carrier network, with BXML call control, bidirectional WebSocket media streams, recording, transcription and transfers. 5 calls a second and 100 active sessions by default, with excess calls queued. Number rental and SIP trunking prices aren't published.

- Page: https://www.anchorterminal.com/tools/bandwidth-voice · Markdown: https://www.anchorterminal.com/tools/bandwidth-voice.md · JSON: https://www.anchorterminal.com/api/v1/tools/bandwidth-voice.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer · endpoint: `https://voice.bandwidth.com/api/v2`

### 212. Sinch Voice API + MCP, B (62.8)

Programmable voice over PSTN, SIP and WebSocket streams, driven by SVAML call-control JSON. Voice API v2 with bidirectional PCM streams and a text relay that handles barge-in. Two API generations with different hosts, auth and markup, and v1 release notes stop in 2022.

- Page: https://www.anchorterminal.com/tools/sinch-voice · Markdown: https://www.anchorterminal.com/tools/sinch-voice.md · JSON: https://www.anchorterminal.com/api/v1/tools/sinch-voice.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer · endpoint: `https://voice.api.sinch.com/v2`

### 246. Infobip Calls API + MCP, C (60.5)

Event-driven call control for PSTN, SIP, WebRTC and WhatsApp legs, with conferences, recording and WebSocket media streaming for external bots. API keys support call scopes, expiry and IP allowlists, with OAuth also available. US outbound calls cost about $0.067 a minute.

- Page: https://www.anchorterminal.com/tools/infobip-calls · Markdown: https://www.anchorterminal.com/tools/infobip-calls.md · JSON: https://www.anchorterminal.com/api/v1/tools/infobip-calls.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer · endpoint: `https://api.infobip.com/calls/1`

### 248. Plivo Voice API, C (60.4)

REST and XML call control for inbound and outbound PSTN calls, with bidirectional WebSocket audio streams, SIP trunking, recording and conferencing. US outbound at $0.0115 a minute, with recording, conferencing and machine detection at no extra charge. 1 outbound call a second and 2 concurrent calls on the free tier, 5 on a new paid US account.

- Page: https://www.anchorterminal.com/tools/plivo-voice · Markdown: https://www.anchorterminal.com/tools/plivo-voice.md · JSON: https://www.anchorterminal.com/api/v1/tools/plivo-voice.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer · endpoint: `https://api.plivo.com/v1`

### 270. Vonage Voice API + MCP, C (59.1)

Voice API that controls calls with NCCO, a JSON list of actions such as talk, input, record, connect and transfer. Websocket audio as 16-bit linear PCM at 8, 16 or 24 kHz, both directions. First call needs an application, a private key and a signed JWT.

- Page: https://www.anchorterminal.com/tools/vonage-voice · Markdown: https://www.anchorterminal.com/tools/vonage-voice.md · JSON: https://www.anchorterminal.com/api/v1/tools/vonage-voice.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer · endpoint: `https://api.nexmo.com/v1`

### 346. Voximplant, D (51.9)

Serverless platform for programmable calling. Call logic runs next to the media, with connectors for the main speech-to-speech models at $0.004 a minute. Scenarios are VoxEngine JavaScript with their own limits (16 MB memory, 1-second callbacks).

- Page: https://www.anchorterminal.com/tools/voximplant · Markdown: https://www.anchorterminal.com/tools/voximplant.md · JSON: https://www.anchorterminal.com/api/v1/tools/voximplant.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer · endpoint: `https://api.voximplant.com/platform_api`

### 424. Exotel Voice API + MCP, E (39.8)

Indian cloud telephony API for click-to-call, call flows, virtual numbers (ExoPhones), SIP trunking and AgentStream, which streams call audio to your bot over WebSocket in both directions. Local Indian numbers and DLT and TRAI handling. Per-minute rates and plan prices not published.

- Page: https://www.anchorterminal.com/tools/exotel-voice · Markdown: https://www.anchorterminal.com/tools/exotel-voice.md · JSON: https://www.anchorterminal.com/api/v1/tools/exotel-voice.json
- Capabilities: voice.calls, voice.numbers, voice.streaming, voice.sip, voice.recording, voice.transfer · endpoint: `https://api.exotel.com/v1`

## How we test this category

Inbound and outbound call setup, bidirectional audio streaming, a warm transfer and a recording on every API. We watch webhook reliability, note which countries numbers are available in, and price a five-minute call end to end. This test hasn't run yet, so Task success is pending and the grades here come from the categories assessed from public evidence.

## Indexed, not reviewed (3)

Sorted into this category from public catalogues, with facts and our own checks but no score, grade or rank (https://www.anchorterminal.com/indexed/index.md).

| Listing | Kind | What it does | Why it's here |
| --- | --- | --- | --- |
| [callmcp.ai MCP server](https://www.anchorterminal.com/tools/callmcp-server.md) | MCP server | One MCP tool contract for telephony — any call provider, hosted, local, or BYOK. | vendor's own |
| [Chamade](https://www.anchorterminal.com/tools/chamade-server.md) | MCP server | Voice and chat for AI agents — Discord, Teams, Meet, Slack, Zoom, Telegram, WhatsApp, NC Talk, SIP | vendor's own |
| [ToughTongue AI](https://www.anchorterminal.com/tools/toughtongueai-mcp.md) | MCP server | Create voice-agent scenarios, pull session analytics, place SIP calls, schedule meeting bots. | vendor's own |