ONSIM Launch the Customer API (V1)

Our Customer API is live. Read the API docs or keep reading for what’s in V1.

Your network data, in your own systems

Back in 2020, when we launched our 4G Landline SIM, we promised an API that would let customers pull their call, data and SMS logs into their own platforms. It’s taken longer than we’d like to admit, and a redesigned calling and billing platform along the way, but it’s here.

The ONSIM Customer API lets your CRM, data warehouse, compliance tooling or in-house apps read your ONSIM account directly. No CSV exports, no screen-scraping the dashboard, no waiting on a monthly bill to find out what happened.

Every ONSIM call passes through our own call-handling platform, so the API isn’t reading a billing extract. It’s reading the call events that platform records in real time, connected or not, which is why you get things most networks simply don’t give you.

What’s in V1

Calls, with every leg. A call isn’t one line on a bill. It rings a hunt group, gets passed to an IVR, goes to a colleague’s mobile, ends up in voicemail. The API returns each call as a tree of legs, so you can see exactly who it rang, who answered, who it was passed on to and when.

Missed and unanswered calls. Every call has an outcome - answered, missed, abandoned or unanswered - and every leg has its own. That includes outbound calls that rang out and never connected, the calls mainstream networks don’t log because there’s nothing to bill.

Recordings. If you record your calls with us, each recorded leg is available over the API as a WAV file, delivered through a short-lived download link.

Your account structure. Users, numbers, hunt groups and IVRs, plus the services attached to any user or number - useful for keeping an internal directory or asset register in sync without re-keying it.

Data sessions. Mobile data usage per session, for anyone reconciling data use across a fleet of SIMs.

Charges. Calls and legs carry their charge where there is one, so finance teams can allocate costs by user, department or customer without waiting for an invoice.

Read-only, on purpose

V1 reads. It does not change your account, send a message or change how a call routes.

That was a deliberate choice. Most customers asking us for an API want their data out, not another way to reconfigure their phones. Keeping V1 read-only means a key sitting in a reporting tool or a third-party integration can never take a line down or divert your calls, and it makes saying yes to your security team a lot easier.

Built to be boring to integrate with

• One key per business. Created by the account owner or a Super Admin in app.onsim under Settings → API, sent in an x-api-key header. It belongs to your company, not to whoever created it, so it doesn’t break when someone leaves.
• Instant rotation and revocation. Regenerate or revoke a key and the old one stops working immediately.
• Stable versioning. Within v1 the API only grows. Breaking changes only ever ship as a new version, and every release is checked against the published contract before it goes out.
• Standard errors. Every error is an RFC 9457 problem document, so your code handles them the same way everywhere.
• Clear limits. Rate limits and a daily quota per key are published in the docs, so you can design your sync jobs around them rather than discovering them in production.

Getting your users is one line:

curl https://api.customer.onsim.uk/v1/users \
  -H "x-api-key: $ONSIM_API_KEY"

What people are building with it

• CRM call logging - attach every call, including the ones that weren’t answered, to the right contact or deal.
• Proof of contact - couriers, trades and recruiters evidencing that a call attempt was made, with a timestamp from the network rather than a handset log.
• Recording archives - pulling recordings into your own storage or compliance platform on your schedule.
• Missed-call reporting - spotting which hunt groups and IVR routes are losing callers, and when.
• Cost allocation - charging calls and data back to departments, sites or end customers.

What’s next

V1 is pull-based: your systems ask for calls and recordings on a schedule. Webhook delivery as calls complete is on our roadmap, but we don’t have a date to commit to yet, and we’d rather say that than promise one we might miss. If you need recordings pushed to you today, our SFTP feed already does that.

Within V1, expect the API to keep growing as we add more of what’s in the dashboard.

Get started

1. Log in to app.onsim.uk as the account owner or a Super Admin.
2. Go to Settings → API and create your key. Store it somewhere safe - it’s only shown once.
3. Follow the API docs to make your first request.

Not an ONSIM customer yet? Get a quote or talk to our team about what you want to connect.