Best of · Voice & speech
Best phone calling and voice transport APIs for AI agents
The 10 highest-scoring of 13 phone calling and voice transport APIs on the Anchor benchmark, with a pick for each need and where each one falls short. Scores come from public evidence, re-checked as vendors change.
- 13 ranked
- 2 agent-ready
- 10 hosted endpoints
- Updated 9 October 2026
Top three
Picks by need
Worked out from the scores, prices and facts, so they change when the research does.
Highest score overall
Twilio Programmable Voice API + MCP A
A, 80.4/100 on the benchmark.
Also Telnyx Voice API + MCP, BB, 74.2/100.
Schema & documentation
93/100 on schema & documentation, against 92 for the overall leader.
Agent ergonomics
90/100 on agent ergonomics, against 80 for the overall leader.
Maintenance & community
90/100 on maintenance & community, against 85 for the overall leader.
The shortlist
| # | Tool | Grade | Best for | Price | Where |
|---|---|---|---|---|---|
| 1 | Twilio Programmable Voice API + MCP Twilio |
A 80.4 | Teams that want the widest number coverage and a managed speech layer (ConversationRelay) behind one vendor, or a published SLA. | $1.15 / mo | hosted and local |
| 2 | Telnyx Voice API + MCP Telnyx |
BB 74.2 | Cost-sensitive US outbound voice agents and for agents that must onboard and pay without a person. | $1 / mo | hosted and local |
| 3 | LiveKit Telephony LiveKit Incorporated |
B 67.5 | Teams that already run voice agents on LiveKit and want phone calls to arrive in the same rooms, bringing their own carrier for outbound and international calls. | $1 / mo | local |
| 4 | SignalWire Voice API SignalWire |
B 67.1 | Builders who want call logic in documents (SWML) or a hosted AI agent verb, and for teams moving off Twilio's API shape. | $0.50 / mo | local |
| 5 | DIDWW Voice and Number Management API DIDWW Ireland Limited |
B 65.1 | Teams that run their own SIP system, or a voice agent platform that accepts SIP trunks, and need numbers in many countries with compliance records handled through an API. | Pay per use | hosted |
| 6 | Bandwidth Voice API + MCP Bandwidth |
B 63.7 | US and Canada outbound voice agents that need capacity from day one and a carrier-owned network. | Pay per use | hosted and local |
| 7 | Sinch Voice API + MCP Sinch |
B 62.7 | Teams already on Sinch messaging, or voice agents that want a managed STT and TTS relay with barge-in without running their own speech stack. | Pay per use | hosted and local |
| 8 | Plivo Voice API Plivo |
C 60.4 | Cost-sensitive voice agents built on Pipecat, LiveKit, Vapi or Retell, and for India traffic. | $0.50 / mo | hosted |
| 9 | Infobip Calls API + MCP Infobip |
C 60.3 | Teams already on Infobip messaging, or that need one vendor for PSTN, SIP, WebRTC and WhatsApp calling across many countries with tightly scoped keys. | Pay per use | hosted |
| 10 | Vonage Voice API + MCP Vonage (Ericsson) |
C 58.9 | Voice agents that want 16 or 24 kHz linear PCM over the websocket and per-second billing. | Pay per use | hosted and local |
3 more are ranked in the full table.
How to choose
- Number availability by countryCheck which countries and number types are available, since an agent cannot place or receive calls in a country where you cannot buy a number.
- Webhook reliability and retriesCheck whether call events are retried when your endpoint is down and arrive in order, since a missed hang-up can leave the agent holding a dead call.
- Audio streaming over websocket or SIPCheck whether bidirectional audio streams over a websocket or SIP trunk, and what codec and sample rate you receive, since a mismatch adds delay or garbled speech.
- Full cost of a callPrice a complete call including connection, per-minute, recording, transfer and speech charges, because the headline rate may cover only part of the bill.
How the benchmark tests 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.
Each one in detail
Twilio Programmable Voice API + MCP
A 80.4/100Programmable Voice for placing and answering calls on Twilio numbers in 100+ countries, controlled with TwiML or REST.
Verdict 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.
Choose it for Teams that want the widest number coverage and a managed speech layer (ConversationRelay) behind one vendor, or a published SLA.
Strengths
- Twilio APIs SLA at 99.95 per cent for every paying customer, with 10 per cent credits
- Restricted API keys with up to 100 endpoint permissions each
- Public OpenAPI specs, llms.txt with Markdown twins, and a numbered error dictionary
Weaknesses
- US outbound at $0.014 a minute, plus $0.0044 for Media Streams or $0.07 for ConversationRelay
- 1 outbound call a second per account by default
- No idempotency key on call creation
Price $1.15 / moAuth OAuth or keyx402 nohosted and local
Telnyx Voice API + MCP
BB 74.2/100Carrier-owned Voice API (Call Control and TeXML) for calls, numbers, websocket media streaming, recording and transfers on Telnyx's own network.
Verdict 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.
Choose it for Cost-sensitive US outbound voice agents and for agents that must onboard and pay without a person.
Strengths
- About $0.007 a minute all-in for US outbound ($0.002 Voice API plus $0.005 termination)
- Bot signup, API key creation and x402 or MPP account top-ups without a browser
- 30 outbound dials a second, Retry-After on 429, and command_id to de-duplicate retried call commands
Weaknesses
- x402 and MPP only top up credit, they don't pay per call
- No free credit, a new account starts at zero
- No scoped or read-only API keys found, and the MCP can dial and buy numbers without confirmation
Price $1 / moAuth OAuth or keyx402 partialhosted and local
Full assessment · Against #1, Twilio Programmable Voice API + MCP
LiveKit Telephony
B 67.5/100LiveKit Telephony connects phone calls to LiveKit rooms as SIP participants. On LiveKit Cloud it covers SIP trunks to outside carriers, US inbound phone numbers, dispatch rules and transfers, managed through a Twirp API, server SDKs and the lk CLI.
Verdict Signed tokens separate the right to dial (sip.call) from the right to manage trunks (sip.admin), and per-minute prices are public with a free plan that needs no card. LiveKit's own phone numbers are US only and inbound only, so outbound calls need a third-party SIP trunk, and no 429 or retry guidance was found.
Choose it for Teams that already run voice agents on LiveKit and want phone calls to arrive in the same rooms, bringing their own carrier for outbound and international calls.
Strengths
- Token grants separate
sip.call(dial and transfer) fromsip.admin(trunks, dispatch rules, numbers), with a lifetime the issuer sets - Free Build plan with no card has one US local number, 50 inbound minutes and 1,000 third-party SIP minutes a month
- Per-minute and per-number prices are public, also as Markdown at livekit.com/pricing.md
Weaknesses
- LiveKit Phone Numbers are US only and inbound only, and
TransferSIPParticipantdoes not work on them yet - Outbound calls need a trunk from another carrier, billed by that carrier on top of LiveKit's SIP minutes
- No 429, Retry-After or idempotency guidance was found for the SIP API, so a retried
CreateSIPParticipantmay dial twice
Price $1 / moAuth API keyx402 nolocal
Full assessment · Against #1, Twilio Programmable Voice API + MCP
SignalWire Voice API
B 67.1/100Programmable calling API from the team behind FreeSWITCH.
Verdict 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.
Choose it for Builders who want call logic in documents (SWML) or a hosted AI agent verb, and for teams moving off Twilio's API shape.
Strengths
- SWML documents, REST commands and a Relay WebSocket client for call control
- OpenAPI 3.1 spec and Markdown for every docs page
- SLA of 99.95 per cent monthly uptime on every account, plus ISO 27001, SOC 2 Type 2, a DPA and a disclosure policy
Weaknesses
- Status page renders only with JavaScript, so its history isn't readable by agents
- No published rate-limit numbers beyond the trial's 10 queued calls
- No idempotency key, and the safe-retry rules live in the Python SDK rather than the API docs
Price $0.50 / moAuth API keyx402 nolocal
Full assessment · Against #1, Twilio Programmable Voice API + MCP
DIDWW Voice and Number Management API
B 65.1/100DIDWW is a telecoms carrier selling phone numbers in more than 90 countries with inbound and outbound SIP trunking. Its REST API v3 orders numbers and configures trunks and capacity, and a remote MCP server covers the same account tasks.
Verdict An OpenAPI 3.0.3 document with 107 operations, Markdown docs, a free sandbox and SDKs in seven languages cover number ordering and SIP trunk set-up. No per-number or per-minute price is public, API keys carry no scopes, orders have no idempotency key, and outbound calling needs an approved application. Calls travel over SIP only.
Choose it for Teams that run their own SIP system, or a voice agent platform that accepts SIP trunks, and need numbers in many countries with compliance records handled through an API.
Strengths
- A public OpenAPI 3.0.3 document describes 107 operations on 67 paths, and 105 of them carry a description of purpose and behaviour
- Every docs page has a Markdown twin, with llms.txt indexes on both sites, an OpenAPI discovery manifest and an MCP server card
- A sandbox at
https://sandbox-api.didww.com/v3is free, separate from production, and funded with Stripe test cards
Weaknesses
- No per-number or per-minute price is published. Price lists are sent on request or shown inside an account, and a $30 balance is needed before ordering
- REST API keys reach the whole account. An optional source IP allow list is the only restriction, with no scopes and no read-only key
- No idempotency key was found on
POST /orders, which charges the prepaid balance at once, so a retried request can buy twice
Price Pay per useAuth API keyx402 nohosted
Full assessment · Against #1, Twilio Programmable Voice API + MCP
Bandwidth Voice API + MCP
B 63.7/100Programmable voice on Bandwidth's own US carrier network, with BXML call control, bidirectional WebSocket media streams, recording, transcription and transfers.
Verdict 5 calls a second and 100 active sessions by default, with excess calls queued. Number rental and SIP trunking prices aren't published.
Choose it for US and Canada outbound voice agents that need capacity from day one and a carrier-owned network.
Strengths
- 5 calls a second and 100 active sessions by default, with excess calls queued
- No-card Build trial with 3,000 credits, a US number and SIP trunking
- OAuth 2.0 client credentials with 1-hour tokens, per-credential roles and secret rotation
Weaknesses
- Number rental and SIP trunking prices aren't published
- No bug bounty, security.txt or callback signing found
- LAX and JFK datacentre incidents hit voice for about 7 and 5 hours in August
Price Pay per useAuth OAuthx402 nohosted and local
Full assessment · Against #1, Twilio Programmable Voice API + MCP
Sinch Voice API + MCP
B 62.7/100Programmable voice over PSTN, SIP and WebSocket streams, driven by SVAML call-control JSON.
Verdict 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.
Choose it for Teams already on Sinch messaging, or voice agents that want a managed STT and TTS relay with barge-in without running their own speech stack.
Strengths
- Voice API v2 with bidirectional PCM streams and a text relay that handles barge-in
- Idempotency-Key on v2 call, batch and service writes, with a 10-minute replay window
- OpenAPI file for v2, and official SDKs in four languages, with v2 in Node 1.6.0 and Python 2.2.0 since September
Weaknesses
- Two API generations with different hosts, auth and markup, and v1 release notes stop in 2022
- No published voice rate limits or SLA, and 429 handling is described only in SDK changelogs
- Public pricing is a spreadsheet download plus illustrative examples
Price Pay per useAuth OAuth or keyx402 nohosted and local
Full assessment · Against #1, Twilio Programmable Voice API + MCP
Plivo Voice API
C 60.4/100REST and XML call control for inbound and outbound PSTN calls, with bidirectional WebSocket audio streams, SIP trunking, recording and conferencing.
Verdict 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.
Choose it for Cost-sensitive voice agents built on Pipecat, LiveKit, Vapi or Retell, and for India traffic.
Strengths
- US outbound at $0.0115 a minute, with recording, conferencing and machine detection at no extra charge
- Bidirectional audio streams in linear PCM at 8, 16 or 24 kHz or mu-law at 8 kHz
- Published limits per plan, including concurrency and what happens above them
Weaknesses
- 1 outbound call a second and 2 concurrent calls on the free tier, 5 on a new paid US account
- No OpenAPI spec, availability SLA or DPA found
- No MCP server that can place calls, the official one searches docs only
Price $0.50 / moAuth API keyx402 nohosted
Full assessment · Against #1, Twilio Programmable Voice API + MCP
Infobip Calls API + MCP
C 60.3/100Event-driven call control for PSTN, SIP, WebRTC and WhatsApp legs, with conferences, recording and WebSocket media streaming for external bots.
Verdict API keys support call scopes, expiry and IP allowlists, with OAuth also available. US outbound calls cost about $0.067 a minute.
Choose it for Teams already on Infobip messaging, or that need one vendor for PSTN, SIP, WebRTC and WhatsApp calling across many countries with tightly scoped keys.
Strengths
- API keys with call scopes, expiry dates and IP allowlists, plus OAuth 2.0
- Read-only scopes such as
calls:recording:readandvoice:logs:read - ISO 27001 and SOC 2 Type 2, a data retention notice and a sub-processor list with change alerts
Weaknesses
- US outbound at about $0.067 a minute, several times Plivo, SignalWire or Telnyx
- No published Calls API rate limits or SLA
- Official JavaScript and Python SDKs last released in 2023
Price Pay per useAuth OAuth or keyx402 nohosted
Full assessment · Against #1, Twilio Programmable Voice API + MCP
Vonage Voice API + MCP
C 58.9/100Voice API that controls calls with NCCO, a JSON list of actions such as talk, input, record, connect and transfer.
Verdict 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.
Choose it for Voice agents that want 16 or 24 kHz linear PCM over the websocket and per-second billing.
Strengths
- Websocket audio as 16-bit linear PCM at 8, 16 or 24 kHz, both directions
- Per-second billing on every call
- Short-lived application JWTs whose ACLs can limit a token to named paths and methods, and signed webhooks with a body hash
Weaknesses
- First call needs an application, a private key and a signed JWT
- No Voice API rate limit or SLA found, and the error catalogue's throttling advice is to wait an amount that differs per API
- Pricing page returns 403 to automated requests, rates live in a spreadsheet
Price Pay per useAuth OAuth or keyx402 nohosted and local
Full assessment · Against #1, Twilio Programmable Voice API + MCP
Head to head
- Telnyx Voice API + MCP vs Twilio Programmable Voice API + MCP BB 74.2 vs A 80.4
- LiveKit Telephony vs Twilio Programmable Voice API + MCP B 67.5 vs A 80.4
- SignalWire Voice API vs Twilio Programmable Voice API + MCP B 67.1 vs A 80.4
- DIDWW Voice and Number Management API vs Twilio Programmable Voice API + MCP B 65.1 vs A 80.4
- LiveKit Telephony vs Telnyx Voice API + MCP B 67.5 vs BB 74.2
- SignalWire Voice API vs Telnyx Voice API + MCP B 67.1 vs BB 74.2
- DIDWW Voice and Number Management API vs Telnyx Voice API + MCP B 65.1 vs BB 74.2
- LiveKit Telephony vs SignalWire Voice API B 67.5 vs B 67.1
- DIDWW Voice and Number Management API vs LiveKit Telephony B 65.1 vs B 67.5
- DIDWW Voice and Number Management API vs SignalWire Voice API B 65.1 vs B 67.1
Questions
What are the highest-rated phone calling and voice transport APIs for AI agents?
Twilio Programmable Voice API + MCP has the highest benchmark score of the 13 ranked phone calling and voice transport APIs, 80.4 (A). Telnyx Voice API + MCP is second with 74.2 (BB).
How many phone calling and voice transport APIs are agent-ready?
2 of the 13 ranked here grade BB or better, the bar for agent-ready on the Anchor benchmark.
Which phone calling and voice transport APIs accept x402 payments?
None of the ranked listings here accepts x402 for its main call yet.
How is this list ranked?
By the Anchor benchmark score out of 100, a weighted mean of the scored categories minus deductions for negative events, from public evidence re-checked as vendors change. Listings cannot pay for a place. The latest assessment behind this page is from 9 October 2026.
How this list is made
The order is the Anchor benchmark score, the same number as on each listing and in the top list. Each listing is graded from public evidence against the benchmark checklist, and the picks above are worked out from those grades, prices and facts. No listing pays for its place, and paid audits or listing help never change a score.
Full ranked table · 78 head-to-head comparisons · Best tools in every category