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Various logos of UK mobile networks

Three's unlimited data for £20 SIM only deal: it's the offer of the year

Three phone and SIM card

We run through the benefits of Three's unlimited data SIM only plan that's currently on offer for just £20 a month. SIM Sherpa is your trusty guide. Last updated: February 6th 2019.

What's the deal?

Three unlimited data SIM only

Unlimited everything for £20 a month  (4.5/5)

Three SIM card

It's unlimited data. And it's £20. There's no cheaper unlimited everything SIM on the market.

Plus you're getting Three's usual benefits of 99% 4G population coverage, inclusive roaming and perks like free easyJet upgrades and their daily rewards app, Wuntu.

Useful link: Read our full benefits below

Unlimited
minutes
+
Unlimited
texts
+
Unlimited
4G data
=
£20 a month
on a 12-month contract
(opens in new tab)

What's good about it?

It's genuinely unlimited data - and that's extremely rare

Three offer banner

On a 12-month contractSee full deal

at Three.co.uk
(opens in new window)

If you've ever put your phone down because you're worried about going over you data usage limits, Three's unlimited data SIM puts an end to that. You're free to use as much as you like in the UK at no extra cost.

And you're not limited by any sneaky traffic management or throttling rules when you use it in this country either. Others sometimes promise no data caps but then slow you down to stop you using too much.

You can also use it for tethering (personal hotspot), which is where you connect tablets or laptops to your phone so they can access internet anywhere you have mobile signal. That's unlimited in the UK too.

The only restrictions come when you're using your SIM abroad. There, you won't be able to use tethering, a monthly cap of up to 19GB applies (depending where you are) and Three reserve the right to slow down your connection while roaming.

Useful link: Three's terms and conditions

Three's network offers good 4G coverage and speeds

Three's network map

Make sure you'll be able to use unlimited dataCheck Three's coverage

at Three.co.uk
(opens in new window)

It's true that Three aren't the UK's largest network but they now put their 4G coverage as reaching 99% of the population in the places where they live. There's still work to do in rural locations.

We'd always recommend checking any network's coverage before you sign up. Use Three's official network map here to do so. Be sure to look not just at home but anywhere you'll be using your phone.

Over 4G, we'd expect Three customers to get download speeds of around 20 Mbps on average, which currently puts them in joint second with Vodafone behind EE.

This is a healthy score that is similar to what many will be getting home over non-fibre broadband. It'll support smooth video and audio streaming and let you browse the general internet

Useful link: Check Three signal in your area

The £20 price smashes Three's competition out of the park

EE SIM only offer banner

EE's best deal for £20 is 20GBSee this deal

at EE.co.uk
(opens in new window)

The only other mobile network to offer truly unlimited data is Virgin Mobile and you need to be a Virgin Media TV or broadband customer to be able to buy it. It costs £25 at the time of writing.

Otherwise for £20 a month on a 12-month contract with other mobile networks, you're looking at deals with capped data allowances and you could end up spending more:

Useful link: Use our SIM only deals comparison tool

It's Three's best price for unlimited data for years

Three's Black Friday offer banner

The last time we saw the offer was Black FridayGet deal now

at Three.co.uk
(opens in new window)

The last thing to say is that this isn't one of those offers we see all the time from mobile networks. The last time we saw it from Three was Black Friday, so they're genuinely pulling out all the stops here.

The previous best offer for £20 was a huge 100GB data SIM, which has been paused during the unlimited data promotion. You have to go back years for unlimited data £20 or under.

For most of last year, the regular established price for Three's 12-month unlimited data SIM was £27 a month, which was also down from £32 previously charged too.

The indications from Three are that this will be a temporary offer but we do not have a fixed end date for it that we can inform you about yet.

Useful link: See Three's SIM only deals page

SIM Sherpa can help you find your next SIM only deal

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