Ultravox on a Jamaican Number: Connect Your WOCOM Line over SIP

Ultravox is a voice AI platform built around a model that listens to speech directly, rather than converting it to text first. It has SIP built in, so a Jamaican number carried by WOCOM can ring straight through to an Ultravox agent.

What You Need

• A WOCOM number on Cloud PBX or a SIP trunk.
• An Ultravox account, an API key and an agent you have tested.

Step 1: Get Your SIP Domain

Call GET https://api.ultravox.ai/api/sip with your API key in the X-API-Key header. The response includes a read-only domain for your account. Calls to an agent are addressed as:

sip:agent_{agent_id}@{domain}

The default transport is UDP. Add ;transport=tcp or ;transport=tls if you want those instead. If you would rather WOCOM send your phone number as the user part, Ultravox can match it with an allowedAgents pattern (toUserPattern), and send anything that does not match to a fallbackHandler webhook.

Step 2: Restrict Who Can Send Calls

In the same SIP configuration, set allowedCidrRanges to WOCOM's signalling addresses, which WOCOM support will give you. Ultravox will then reject calls from anywhere else. Alternatively, Ultravox can register to your trunk like a phone, using a username, password and proxy that WOCOM issues.

Step 3: Ask WOCOM to Route the Number

Send WOCOM support the following:

• The Jamaican number(s) you want answered by the AI, written in E.164 form (for example +1876XXXXXXX or +1658XXXXXXX).
• The platform's SIP address for inbound calls (shown below for this platform).
• Whether the AI also needs to place outbound calls, and from which number.
• Where calls should go if the AI hands a caller to a person: an extension, a ring group, or a mobile number.

Ultravox accepts G.711 (PCMU/PCMA), G.722 and several other codecs including Opus. Calls offering only other codecs fail, but WOCOM's standard G.711 and G.722 are both on the list. Ask for G.722 for wideband audio.

Outbound Calls

To place a call, create it with medium.sip.outgoing: the destination (for example sip:+1876XXXXXXX@your-wocom-gateway), your caller ID in from, and the SIP username and password WOCOM issued.

Transfers

Ultravox documents four ways to pass a caller on:

• Cold REFER: hands the call to the target and drops out.
• Warm REFER: the agent introduces the caller first.
• Try REFER: attempts REFER and falls back to bridging if the carrier refuses.
• Bridged: Ultravox stays in the middle. It always works, but Ultravox bills both legs.

Ask WOCOM to allow REFER on your route so you can use the cheaper REFER options.

What It Costs (November 2026)

Ultravox listed about US$0.05 per minute for the call, plus SIP at US$0.005 per minute on pay-as-you-go (slightly less on Pro), billed in 6-second steps. WOCOM call charges apply as normal.

Is Ultravox Right for You?

Ultravox suits developers who want fast, natural turn-taking without managing separate speech and voice providers. For a ready-made receptionist, WOCOM AI is included with Cloud PBX. See the full guide, or contact WOCOM to route your number.