UCaaS - Cloud Business Phone System
UCaaS (Unified Communications as a Service) is a cloud business phone system: extensions, users with multiple devices, programmable call routing, voicemail, and call forwarding, without on-premise PBX hardware. SIP.IO’s UCaaS is API-first: every extension, device, and forwarding rule is a row you can read and write over /v1, not a setting buried three menus deep in an admin GUI.
What you can do
- Give every person an extension. Internal short codes route caller-to-caller, or from an inbound DID, to a user, ring group, queue, voicemail, or flow.
- Let one user carry many devices. A desk phone, a mobile app, and a browser-based softphone can all belong to the same user and ring together.
- Choose how a user rings. Simultaneous (ring all reachable devices), sequential (in
ring_order), or specific (only opted-in devices); a device can also be excluded from the fork entirely while staying reachable for a direct dial. - Set do-not-disturb and forwarding. Forward always, on busy, or on no-answer, to another user, a queue, voicemail, or an external mobile number.
- Build an IVR without touching infrastructure. Menus, business-hours conditions, and branching logic run on the platform’s call-flow engine.
- Give every user a voicemail box. Greeting, PIN-protected retrieval, storage quota, and email notification on a new message.
The user and device model
A user (sip_user) is a person; a device (sip_device) is a registered endpoint, a desk phone, an app, or a browser softphone. One user can have many devices. When a call targets the user, SIP.IO finds their reachable devices and forks to them per ring_strategy (simultaneous by default, or sequential/specific), after evaluating do-not-disturb and forwarding rules in order: fwd_always routes immediately, dnd diverts to busy handling, otherwise the devices ring and a no-answer falls to fwd_noanswer or voicemail. The user’s internal caller-ID is stamped on every fork leg, so an extension-to-extension call always shows who’s calling.
Numbers reach this model through the same route target every object shares: a DID or extension points at dest_kind: "user" (or ring_group, queue, voicemail, forward, and more), with business hours optionally attached directly to the number so after-hours or holiday calls override the normal destination. See DID Numbers and SIP Trunking for how calls, PSTN or BYOC, arrive at those numbers in the first place.
For anything past simple extension-to-extension and forward rules, an IVR menu, a time condition, an HTTP lookup, point the number at a call flow instead of a direct target; the platform runs both through the same interpreter, so you can start simple and add branching later without re-plumbing anything.
Capability table
| Capability | Docs |
|---|---|
| Users, multi-device ring, DND, forwarding | Users & Devices |
| Extensions & DIDs, route targets, business hours | Numbers & Extensions |
| Call flows / IVR (menus, conditions, nesting) | Call Flows |
| Voicemail boxes, greetings, retrieval | Voicemail |
| External forwarding with press-1 screening | Call Forwarding |
| Browser-based softphone as a device | Embedded Softphone (WebRTC) |
Secure by default
Voicemail recordings sit in a private bucket served only through an IP-gated media proxy, never world-readable. PINs for voicemail retrieval are stored as key-value secret references, never plaintext. Forwarded legs and every other outbound hop ride the same signaling and media protections as the rest of the platform.
FAQ
What is UCaaS? A cloud-hosted business phone system: extensions, multi-device users, call routing, voicemail, and forwarding, delivered as a service instead of on-premise PBX hardware.
Can one user ring more than one device? Yes. Simultaneous or sequential ring across desk phone, app, and softphone devices, with DND and forwarding evaluated first.
Call forwarding to a mobile? Yes, always/busy/no-answer triggers, with press-1 confirm screening so a carrier voicemail can’t swallow the call, and an overflow destination if it still isn’t answered.
This is one PBX/business-phone-system angle on the same user model that powers SIP.IO’s cloud contact center; see the full platform overview for every capability.