SignalWire Voice API vs Voximplant

SignalWire Voice API

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.

Voximplant

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).

SignalWire Voice API

1. Send dial with a url pointing at a SWML document, then use calling.* commands on the returned call ID
2. Don't retry a dial on a 5xx. Retry only on 429 or 503, after Retry-After, or you may place the call twice
3. Use your own Space subdomain as the host, there is no shared API host
4. Create a token with only the Voice scope for a calling agent
5. Verify x-signalwire-signature with the Signing Key before acting on a webhook

Voximplant

1. Upload a VoxEngine scenario and a rule first, then start it with StartScenarios and pass the number in script_custom_data
2. Use a service-account JWT rather than api_key in the URL
3. Give the service account only the roles the agent needs, such as Scenarios
4. Ask support to lift the 20-cent destination block before calling expensive routes