A data-only SIM is a plan with the calls and texts taken out, sold for tablets, routers, dashcams and second devices. The intuition is that removing two thirds of a product should make it cheaper, and the published figures say otherwise: on the one seller in this record that prints both ladders side by side, the data-only plan costs more than the plan with calls and texts included at every tier that appears on both.
The one seller that publishes both ladders
SMARTY prints its full ladder and its data-only ladder on the same page, which makes the comparison exact rather than inferred. With calls and texts: Unlimited £20, 200 GB £17, 150 GB £15, 100 GB £12, 40 GB £10, 20 GB £9, 16 GB £8, 5 GB £6. Data only: Unlimited £20, 100 GB £17, 40 GB £13, 15 GB £9, 2 GB £5. At 40 GB the data-only plan is £13 against £10 for the same data with calls and texts, and at 100 GB it is £17 against £12. The only tier where data-only wins is the very bottom, 2 GB at £5, which is below anything on the other ladder.
Why the cheaper-looking product costs more
Calls and texts cost a network almost nothing to carry and are worth a great deal as a reason to keep you, so they are given away with the data rather than sold beside it. A data-only SIM is bought by someone who has already decided they need it, usually for a device that cannot make calls anyway, and it is priced accordingly. The practical consequence is worth stating plainly: if the device takes a normal SIM, price the ordinary plans first, because on published UK ladders they are usually the cheaper way to buy data.
4G, 5G and what to actually check
Data-only plans are sold as 4G or 5G and the distinction matters less than the allowance for most uses: a router in a house with a decent 4G signal is not improved by a 5G plan it cannot reach. Check the coverage where the device will sit rather than the label on the plan, and check whether the plan allows tethering and personal hotspot, which is the restriction most likely to make a data SIM useless for the job you bought it for. Neither is published on any page read for this record, which is why both are questions to ask before buying rather than facts this site can give you.
Questions people ask about data sim only deals
What do data sim only deals cost?
SMARTY publishes a data-only ladder of Unlimited £20, 100 GB £17, 40 GB £13, 15 GB £9 and 2 GB £5. At most tiers that is more than the same data with calls and texts included on its other ladder.
Is a data only pay as you go sim cheaper?
Usually not. At 40 GB SMARTY publishes £13 data-only against £10 with calls and texts. The only tier where data-only wins in this record is 2 GB at £5, which is below the bottom of the other ladder.
What is the difference between a 4g data only sim and a 5g data sim?
The network generation the plan is sold for. For a fixed device it matters less than the coverage where the device will sit, which is worth checking before the label on the plan.
What do mobile data and sim data mean on a bill?
Both mean the allowance the plan carries, measured in gigabytes. What varies between sellers is what happens when it runs out: SMARTY publishes £1 per GB for an add-on, and most sellers publish nothing.