Programmable Voice API
A programmable voice API lets your software make and receive phone calls and control everything that happens on them: play audio, run an IVR, collect input, record, route, and connect callers to agents or AI, over HTTP and SDKs, no telephony hardware required. SIP.IO is a developer-first voice API that’s also a full contact center, on an anycast-global edge, secure by default, with transparent pricing and a free tier.
What you can build
- IVRs and phone menus: multi-level menus, digit collection, speech prompts in 16 languages.
- Inbound call apps. Route a number to a flow, a user, a queue, or voicemail.
- Outbound calling: notifications, reminders, click-to-call, dialers, via outbound routes and trunks.
- Call recording & voicemail. Capture, store, and notify.
- AI voice agents: stream audio to your model and hand off to a human.
How it works: call flows as data
Instead of returning instructions on every step from your server, you describe the whole call once as a call flow: a JSON node-graph that’s also editable in a visual builder and executed per call at the edge. Branch on DTMF, time of day, conditions, or HTTP lookups.
{ "start": "menu", "nodes": [ { "id": "menu", "type": "menu", "data": { "kind": "menu", "promptText": "Press 1 for sales, 2 for support", "maxDigits": 1, "timeoutSec": 5 } }, { "id": "sales", "type": "enqueue", "data": { "kind": "enqueue", "queueId": "q_sales" } }, { "id": "supp", "type": "voicemail","data": { "kind": "voicemail", "mailboxId": "vm_support" } } ], "edges": [ { "source": "menu", "target": "sales", "sourceHandle": "digit:1" }, { "source": "menu", "target": "supp", "sourceHandle": "digit:2" } ]}See the Flow Node Reference for every node type (menu, collect, dial, enqueue, voicemail, conference, forward, condition, HTTP request, time condition, and more).
Core capabilities
| Capability | Docs |
|---|---|
| Programmable call flows (visual + JSON) | Call Flows · Flow Nodes |
| Numbers & extensions, typed routing | Numbers & Extensions |
| Outbound, BYOC SIP trunks, transforms | Trunks, Outbound & PSTN |
| Voicemail | Voicemail |
| Call forwarding (find-me/follow-me) | Call Forwarding |
| Multilingual TTS | Media & TTS |
| Concurrency & rate control | Concurrency Control |
Why SIP.IO
- Voice + contact center in one. The same API runs IVRs and a full ACD contact center.
- Edge-native: an anycast control plane keeps routing decisions close to the caller.
- Secure by default: TLS signaling and SRTP media.
- Developer-first: SDKs, a full OpenAPI surface, and an OpenAI-API-compatible interface.
FAQ
What is a programmable voice API? It lets software make/receive calls and control them (play, gather, record, route, bridge) over HTTP/SDKs instead of hardware.
How does SIP.IO’s work? You describe calls as a JSON flow (also visual) executed at the edge, or drive calls directly via the API/SDKs.
Inbound and outbound? Both: DIDs for inbound; outbound routes and SIP trunks (incl. BYOC) for outbound.