Twilio Programmable Voice API + MCP vs Vonage Voice API + MCP

Twilio Programmable Voice API + MCP

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.

Vonage Voice API + MCP

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.

Twilio Programmable Voice API + MCP

1. Use <Connect><Stream> for two-way audio. It blocks further TwiML until the websocket closes
2. Use <Connect><ConversationRelay> when you only want to handle text, and set interruptible for barge-in
3. Trial calls reach only verified numbers in your sign-up country
4. Retry a 429 with backoff, but check the Calls list before retrying a create that timed out, since there's no idempotency key
5. Validate X-Twilio-Signature on every webhook and websocket upgrade

Vonage Voice API + MCP

1. Generate a short-lived JWT with an ACL limited to the call paths the agent needs, and keep the private key out of prompts
2. Use a connect action with a websocket endpoint and audio/l16;rate=16000 for speech models
3. Keep the api.nexmo.com hostname, Vonage's llms.txt says not to swap it
4. Enable signed webhooks and verify the HS256 JWT on each event
5. Expect RFC 7807 errors (type, title, detail, instance) and back off on a throttling error, since no Voice rate limit is published