SMARTY's unlimited data SIM for £17.50: is it truly unlimited?
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We look at how SMARTY's unlimited data plan compares with other networks for price, benefits and any restrictions in their fair usage policy. Last updated: 11th September 2025.
What you get
The UK’s most flexible unlimited data plan, now with 5G
(4/5 deal rating, excellent)
We don’t think there’s a more flexible unlimited data plan on the market than SMARTY’s. There’s no long-term contract, just a rolling 1-month plan that you can cancel or change anytime.
You're also free to use the SIM in phones, tablets or mobile broadband routers. As long as it's for personal use, you're not restricted by speed caps or usage limits.
And on offer at £17.50 a month, it's still one of the best value unlimited plans you’ll find anywhere:
Unlimited minutes + Unlimited texts + Unlimited data (5G) = £20 £17.50 a month (1‑month plan, no contract)
See full deal
Useful link: Read our full SMARTY network review here
The benefits
It’s genuinely unlimited data to use how you like in the UK
One of the things we rate most about SMARTY’s unlimited data SIM is how flexible it is, compared to others. First, it’s a rolling monthly plan. That means there are no contracts, no notice periods and no commitment.
You pay up front each month and can stop it whenever you like. That’s perfect if you want to test out SMARTY or the Three network, without being locked in. Even many other 1-month SIMs require you to give notice to leave.
The data itself is truly unlimited for use in the UK. There are no speed caps, throttling, no data limits or hidden fair usage policies. You’re also free to tether as much as you want or use the SIM in tablets, dongles or mobile broadband devices.
Overall, we’d say there’s no other 1-month unlimited data SIM this flexible. And at just £17.50 a month, you’d be hard fought to beat it even on a longer contract.
Useful link: Read our full SMARTY network review
You get full access to Three’s award-winning 5G speeds
We’ve always found coverage and speeds between our SMARTY SIM vs Three ones to be the same, with no built-in differences. That means SMARTY’s SIM gets you the benefit of Three’s UK’s fastest 5G with unlimited data.
SMARTY tell you what kinds of speeds you can expect. Independent testers put typical 5G over the Three network at 208.9 Mbps - 276.17 Mbps, with peak speeds around the 600 Mbps mark. That’s home fibre fast.
Even their 4G downloads should average out at in the high 30 Mbps range. All of which means you could conceivably use your SMARTY unlimited data SIM as a substitute for home broadband.
If you want a fast network to rip through as much data as you like, SMARTY are a decent choice.
Useful link: Check SMARTY’s 5G locations
Restrictions on SMARTY's unlimited data deal
There are some limits on data usage when roaming
SMARTY’s unlimited data really is unlimited for personal use within the UK. There are no speed caps, and you’re free to tether or use the SIM in tablets or mobile broadband devices.
However, like all networks, SMARTY has some checks in place to prevent commercial misuse. If your usage exceeds 1000GB (1TB) in a single month, they may review how you're using the plan.
This isn’t a hard cap. But if it looks like you’re using your SIM in a business setting, such as for providing free WiFi to customers, SMARTY may investigate. Genuine users are unlikely to ever hit 1000GB.
Also, when you’re roaming within the EU there is a 12GB monthly fair use limit. That’s lower than it used to be but still enough for typical short trips. Once you hit that, you’ll need to buy a data add-on if you want to continue using mobile internet abroad.
Useful link: SMARTY's guide to tethering on their network
How SMARTY's deal compares
It's basically always among the best value unlimited SIMs
SMARTY's unlimited deal is almost always among the best priced on the market, particularly when you look at 1-month plans. Sometimes, longer contracts do minorly win out. Here's the latest comparison:
Useful link: Compare all unlimited data SIMs