Prepaid SIM for devices: not every device SIM is a line you can top up
A tablet, a router and a tracker all take a SIM, and all three behave differently at checkout. A watch usually has no line of its own at all, and a managed machine-to-machine plan often has no number to address. Here is how to tell which of those your device is — before you pay, not after.
Start with the line, not the device
A top-up is delivered to a mobile number. The hardware around that number is not something we ever see — but it decides whether there is a number in the first place, which is the whole question on this page.
Worth saying plainly first: no SIM is sold here and no eSIM profile is issued. The card comes from an operator or a seller; what this service does is keep the line behind it loaded. Where a prepaid line comes from in the first place is on the prepaid SIM overview.
Its own prepaid line
The device holds a SIM with its own mobile number and its own balance. Phones, cellular tablets and almost every router are here.
This is the easy case: the number is all a top-up needs, and the device never has to be told anything.
A plan borrowed from another line
The device is connected through an account that belongs to a different number — the companion arrangement most cellular watches use.
There is no second balance to load. Topping up the line it borrows from is what keeps it working.
A managed machine-to-machine plan
Connectivity sold as a service by an IoT provider, administered on their platform and billed to an account rather than to a balance on the SIM.
Frequently there is no number a third party can address. That case has its own section below.
Which device SIMs have a number to top up
Five classes cover almost everything people put a prepaid SIM into. Find yours, then read the last column.
| Device | What the SIM usually is | Its own mobile number? | Can it be topped up here? |
|---|---|---|---|
| Phone — iPhone or Android | An ordinary prepaid line on a consumer network. | Yes, and it is the number people already call. | Yes. |
| Cellular tablet — iPad or Android | Its own prepaid line, separate from the phone in your pocket. | Yes, though it is rarely a number anyone dials. | Yes — it is the tablet's number, not the phone's. |
| Mobile or home router | One prepaid data line that everything in the room shares. | Yes, but it is printed on the pack or shown in the router, not on a screen. | Yes. |
| Cellular smartwatch | Usually a companion plan riding the phone's account, not a line of its own. | Often not — it borrows the phone's number. | Only if the operator gave the watch its own prepaid number. Otherwise top up the phone's line. |
| Tracker, camera or IoT module | Either a consumer prepaid SIM or a managed machine-to-machine plan. | A consumer SIM has one. A managed plan often has none you can use. | The consumer kind, yes. The managed kind, no — see below. |
Where the SIM physically sits, and the four reliable places to read its number when no screen shows one, are set out on the prepaid data SIM page — along with the two validity clocks and what to check when the data does not appear afterwards.
IoT and M2M SIMs are a different product
They look identical — same plastic, same tray — but they are sold on a different model, and that model is what decides whether a top-up can reach one.
How they are sold
By connectivity providers rather than by the consumer arm of a network. The SIMs are administered from the provider's own platform, data is often pooled across a whole fleet instead of sitting on one card, and the bill goes to an account.
Because nothing is held as a balance on the individual line, there is usually nothing on that line to add credit to.
Why the number is the blocker
A top-up is addressed to a mobile number and nothing else. Plenty of machine-to-machine plans are issued without a dialable number at all, or with one locked to the reseller who supplied the SIM.
With no number to address, there is no order to place — not here and not through any other top-up service.
Three checks that tell you which one you have
All three have to come back yes. One no and the provider's platform is the only place to add data.
- The SIM came on a consumer tariff from a network you could walk into a shop and buy from — not from a connectivity provider.
- There is a mobile number attached to it, and you can read it somewhere: the pack, the device, the router page or the operator account.
- That number belongs to you or to whoever asked you to load it — not to a reseller who keeps the line on their own account.
A line that cannot take a load is refused by the operator rather than half-processed. When that happens the full amount, service fee included, goes back to the card automatically and the reason the operator gave is emailed to you — the delivery policy lists every case. So a wrong guess costs time, not money.
One thing this page will not pretend to offer: there is no fleet tooling here. No API, no bulk upload, no per-device dashboard — one order goes to one number. The full list of what a business account does and does not do is on top-up for business.
Watches usually have no second line
The single most common wrong assumption in this whole category, and the easiest one to check.
A cellular smartwatch is normally set up as a companion to a phone: the operator attaches it to the same account and it uses the phone's number. There is no separate prepaid balance sitting on the watch, so there is nothing on it to top up — loading the phone's line is what keeps the watch connected.
Some operators do sell a watch its own prepaid number instead. The test is the same either way: open the operator account and count the numbers on it. Two numbers means the watch has a line of its own, and that line tops up like any other. One number means the watch is riding it.
- Two numbers on the account — top up the watch's own number.
- One number on the account — the watch has no balance of its own; top up the phone.
A router SIM is the whole household on one line
When a 4G or 5G box is the internet rather than a spare, running out stops being an inconvenience for one device and starts being an outage for the house.
Everything shares the allowance
Laptops, a television, a console, every phone on the WiFi — all of it draws on one prepaid line. Sizing that line is a different exercise from sizing a phone's; choosing a bundle size is where that is worked out.
Nobody sees the warning
A phone shows a low-balance message on its own screen. A router has no screen and the operator's text goes to a number nobody reads, so the first sign is usually that the house is offline.
Find the number while it still works
The router's admin page needs the connection you are trying to restore. Read the number now and keep it somewhere else — four places to look covers where it hides.
Devices, question by question
Payment, refunds and account questions are answered in the help centre.
Open the help centreCan I top up a prepaid IoT or M2M SIM here?
Only if it is really a consumer prepaid line with a mobile number you can read. A connectivity provider's managed SIM is topped up on their platform, not by number, and frequently has no usable number at all. The three checks above settle it in under a minute.
My iPad has a SIM. Is that the same number as my iPhone?
No. A cellular tablet with its own SIM has its own line and its own balance, even though nobody ever dials it. Enter the tablet's number, not the phone's — they are separate orders.
Does a smartwatch need its own prepaid SIM?
Usually not. Most cellular watches are attached to the phone's account and use its number, so there is no second line to buy or load. Where an operator has given the watch its own number, that number tops up normally.
Can you send me a SIM for my router?
No — nothing is posted from here. This service adds credit to a prepaid line that already exists, so the SIM has to come from an operator or a seller first. After that, the router's number is all a top-up needs.
The device shows no number anywhere. What do I do?
Try the pack it was punched out of, the device settings, the router's admin page and the operator account, in that order — the data SIM page walks through all four. If none of them produces one, that is itself the answer: a line with no readable number cannot be topped up by anyone but its provider.
Does the device have to be switched on when I pay?
No. The operator applies the credit to the account at their end, so the hardware plays no part in the delivery. It only needs to be on the network afterwards to use what arrived.
Where to go next
This page decides whether there is a line at all. The pages around it take over once there is.
Taking a device abroad instead? Travel SIMs weighs roaming against a local line, and pack shapes explains the daily, weekly and night-only bundles a router or tablet is often offered.
Got the number? The device stops mattering.
Enter it with its country code and the operator's own catalogue opens — the same flow whether that number lives in a phone, a tablet or a box under the stairs.