We went looking for the ultimate unlimited, public-IP IoT SIM: uncapped data, a real IPv4, multi-network, 5G, no contract, no fair-use trap. Did it exist? Almost. Here is the one box nobody can tick, and the architecture that fixes it anyway.
We set out to answer a simple question. Is there a genuinely perfect industrial SIM card out there? The ultimate unlimited, public-IP IoT SIM that does everything a remote 4G or 5G router could ask for?
So we drew up the wish list and went looking. Here is how the candidate scored.
- Uncapped data usage, with no fixed ceiling?YES
- A dedicated public IPv4 address, presented straight on the router?YES
- Genuinely non-NATed, with no carrier-grade NAT in the way?YES
- Multi-network roaming across the UK operators?YES
- Both 4G and 5G?YES
- A 30-day rolling contract, with no lock-in?YES
- No fair-use policy quietly waiting to throttle it?YES
Every box ticked. No throttling, no allowance to trip over, no contract, no NAT, a real routable address and data that simply does not stop.
This, frankly, sounds like the perfect SIM. It is the kind of specification that would solve half the remote-access and failover headaches in industrial connectivity in a single line on an order form. Direct inbound access to a router in the field, on any network, on 5G, with data you never have to think about again.
And the honest answer is yes. We found a SIM that does every one of those things.
The only box we could not tick was a fixed monthly price for all of it.
Yes, it exists. Uncapped, public IP, multi-network, 5G, no contract. The one thing we could not find was all of it for a fixed monthly cost.
Because the package includes 1GB of data for £10 a month, and every gigabyte after that costs £3. There is no cap. Use 1GB or use 10TB, the SIM will not stop and the router will not be cut off for exceeding an allowance. In the most literal sense, the data really is unlimited.
So, unfortunately, is the invoice.
The data is unlimited. So is the bill.
Use 100GB in a month and you would pay around £307. Use 500GB and it is roughly £1,507. The connection never fails. It just quietly bankrupts you. Unlimited data, then, as long as you bring an unlimited budget.
And this is the exact moment that plays out every single time someone searches for an “unlimited fixed-IP SIM”. The headline offer looks like the holy grail. Then you open the terms. There is a fair-use policy. Or a per-gigabyte charge. Or it turns out the tariff only works on one network. That one word, “unlimited”, was doing an enormous amount of quiet work.
“Unlimited” is not one thing
The word gets stapled to at least six different products, and they behave nothing alike once you put them in a permanent installation:
- Unlimited data for a fixed monthly price. The thing everybody actually pictures.
- “Unlimited” with a fair-use policy. A soft or hard limit sitting a few hundred gigabytes up the road.
- Uncapped, pay-as-you-use. No ceiling, but every gigabyte is billed. The £10 SIM above.
- A very large bundle dressed up as unlimited. A fixed allowance sized so most people never reach it.
- Unlimited on one network, restricted when roaming. Fine on the home network, awkward the moment you want multi-network resilience.
- Consumer unlimited. The cheapest headline, and frequently banned outright in routers, in permanent installations or for commercial use.
Here is the part the adverts gently skate over. Most genuinely unlimited SIMs are single-network. They live on one operator, and that is precisely how the price stays low. Multi-network unlimited SIMs do exist, but the moment you add roaming across networks the sums change: expect a cap of around 250GB and a price near £120 a month.
So the specific thing most industrial buyers ask for, unlimited data across multiple networks with a public IP for a low price, is not a product you can buy. It is three or four separate compromises wearing a single word.
Unlimited, multi-network, public IP, cheap. That is not one SIM. It is four compromises sharing one adjective.
| Tariff type | Networks | Monthly cost | Real data ceiling | The catch |
|---|---|---|---|---|
| Metered public-IP SIM | Multi-network | £10 plus usage | None | £3 per GB; the bill scales with use |
| Fixed-price unlimited | Single network | ~£80 | ~500GB FUP | One network; managed down at the fair-use limit |
| Multi-network unlimited | Multi-network | ~£120 | ~250GB | Lower cap, the price of roaming |
| Consumer unlimited | Single network | Varies | Subject to terms | Often prohibits routers and commercial use |
Notice what the table quietly reveals: the single-network unlimited SIM gives you more real data for less money than the multi-network one. Hold that thought, because it matters at the end.
Start with the actual job, not the adjective
Before buying anything, answer one question: what is this connection actually doing? Three jobs cover most industrial deployments, and each wants a different answer.
5G or 4G as a backup line
A failover WAN sits idle most of the month, then carries the entire site the moment the primary circuit drops. The data is spiky and unpredictable, and the whole point is the bad day. You want headroom for the outage, not a per-gigabyte meter that turns a line fault into a surprise invoice. A fixed-price plan, or a generous bundle you will rarely touch, suits this far better than anything metered.
Permanent CCTV and video streaming
This is the one job that genuinely eats hundreds of gigabytes: sustained, round-the-clock upload. It is also where a metered SIM becomes financial self-harm, and where the maths above stops being funny. Size it against a real unlimited or high-bundle plan, and while you are there, ask whether all that video actually needs to leave site. Edge recording with event-only upload can cut the data by an order of magnitude and change which tariff you need in the first place.
Telemetry, metering and occasional maintenance
A PLC sending readings, a meter phoning home, a router you log into now and then. A few megabytes to under a gigabyte a month. These never needed unlimited anything. A small metered plan is the cheapest answer by a distance, and “unlimited” is just money you are handing over for reassurance you do not need.
The sizing rule. Estimate real monthly consumption first, then pick the tariff that makes that number cheapest and most predictable. Low and steady favours a small metered plan. High and sustained favours fixed-price with a fair-use headroom. Spiky or unknown favours whichever plan caps your worst-case bill.
Do you even need a public IP?
Now the other half of the search: the public IP. Before you pay a premium for one, ask what genuinely needs to reach the device from outside.
Very often, nothing does. The kit on the LAN, the PLC, the sensor, the camera’s own cloud client, only ever pushes data outward to a platform. It never accepts an inbound connection. In that scenario a public IP is earning its keep for exactly one purpose: letting you get into the router to manage it.
And you do not need a public IP for that either.
Teltonika’s RMS (Remote Management System) and Robustel’s equivalent cloud platform (RCMS) both hand you the router’s own web GUI, its configuration and its firmware updates over an outbound connection. The router dials out to the platform, and you reach it through the platform. No public IP, no inbound port sitting open to the internet, nothing for a scanner to trip over. For a whole fleet, that usually solves the remote-management problem outright, and the LAN devices behind the router carry on quietly sending their data to the cloud as before.
So for a large share of deployments, the honest answer is: you do not need inbound access at all, and the “public IP” line on the SIM was solving a problem you did not have.
The real holy grail
But some jobs genuinely need a reachable, routable public IPv4 pointing at the router and the network behind it. Direct inbound access, a service you host on site, a protocol that will not tunnel neatly through a management platform. For those, here is the version of the holy grail that actually holds up, and it is not a SIM at all. It is an architecture.
- A 5G router.
- A single-network SIM with genuinely unlimited data. Single-network keeps the price low and the real allowance high, and modern 5G coverage means one well-chosen network is usually plenty.
- A cheap VPS with a static public IPv4 address, around £10 a month.
- A WireGuard tunnel from the router out to the VPS.
The VPS holds the public IPv4. The router connects out to it over WireGuard, so nothing on the internet ever needs to find the router first. You then route inbound traffic that arrives at the VPS through the tunnel to the router, and, where you need it, on to the LAN behind it. The result is a genuine, reachable public IPv4 pointing straight at your router and its devices, without ever buying a public-IP SIM.
Now compare that with the multi-network public-IP unlimited SIM you started out wanting. The VPS route is cheaper. It gives you more real data, because a single-network unlimited SIM out-carries a multi-network one. And it is more secure, because the exposed surface is a hardened server you control, not a router hanging directly off a carrier’s public address for every internet scanner to knock on.
Then lock it down, because you now own the front door
- Deny inbound by default on both the VPS and the router. Open only the WireGuard port, and only forward what genuinely needs forwarding.
- Whitelist source addresses wherever you can, so the tunnel and any exposed service only answer to known hosts.
- Strong authentication everywhere, and no default credentials left anywhere on the router, the VPS or the devices.
- Disable management services you are not using.
- Keep the router firmware and the VPS patched.
- Treat the router as the boundary. Never hang industrial equipment straight off the public side of it.
That is the real answer hiding behind the unlimited-SIM search. The dream product is a single word covering four compromises. What you actually want is a 5G connection sized to the job in front of you, and a public IP you control, on a server you control. Match the architecture to what the site is doing, and “unlimited” turns out to be the least interesting decision on the list.