Best SIM only deals: the latest UK plans for May 2025

The best SIM only deals can be the perfect option for a number of people. Whether you've bagged a bargain SIM-free phone or have reached the end of your contract, now is the time to find a new SIM to jam into your old handset.

Luckily (and no matter the reason you're looking for one), there is a massive range of SIM only deals currently available, ranging from the cheapest plans possible all the way up to the holy grail for streamers and gamers – unlimited data.

If you've been affected by the cost of living crisis, switching to a SIM only plan is a great way to save money on your phone bill and we've found the best providers and prices in our comparison guide below.

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SIM only deals comparison: top deals for May 2025

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Red Pocket Mobile Phone Plan SIM GSMT

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$30

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On top of the wealth of choice, many SIMs now come with both 4G and 5G compatibility meaning those ahead of the game with a 5G handset can find the right option here as well.

For the thrifty shoppers out there, investing in a SIM plan seems to be the best way to save on your phone contract. If you've got the money to put upfront, a SIM-free deal can undercut the cost of a phone contract with ease.

Of course, if you already know exactly what you need, simply make use of the price comparison chart above to find the cheapest options. But if you're still trying to work out your ideal plan, use the below information to find out more.

SIM only deals: the top choice right now

Star Deal

Smarty SIM only | One month rolling plan | Cancel anytime |  Unlimited data, calls and texts | £20/month
We just can't recommend this SIM only deal higher here at T3. We love unlimited everything SIMO deals, and promote them regularly, but we've never seen one as good as this. You get unlimited data, calls and texts for just £20 per month, and what's more, you get it with no contract attached, meaning you can cancel at any time. Simply incredible.

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What is a SIM only deal?

It stands for 'Subscriber Identity Module' but the important thing to know is that a SIM will allow you to make calls, texts and use data from any phone. There are multiple different sizes, prices and caps on calls, texts and data depending on what plan you go for. You can also get data SIMs for tablets, computers and other systems that don't require calls or texts.

This is a great thing to consider if you're on a budget or if you find a cheap phone deal on a retailer site like Amazon, Currys, John Lewis or Very.

Which network is best for me?

EE:
It's both the UK's most popular network and the fastest 4G network, giving it some pretty strong bragging rights. However, where EE tends to fall short in the world of SIM plans is in price. EE phone deals don't tend to be cheap and the same can be said for its SIMs! So if you see a good price on EE, it is worth grabbing.

Vodafone:
Vodafone, much like Three, tends to thrive in the world of SIM only deals. Whether you go straight to the Vodafone website or through a 3rd party retailer, you will find some of the cheapest options on Vodafone. Vodafone's VeryMe service giving out free gifts is yet another reason to join its service. However, if you decide to go for unlimited data on Vodafone, be wary of the speed caps the network can impose.

Three:
Ah Three, for the past year or two this network has dominated the world of SIM only deals. Unlimited data? Three has the best options. Cheap plans? Three is right up there. You will find Three's best SIMs direct from its site.

O2:
O2 doesn't necessarily have a strong USP but what it does have is Priority rewards, securing you everything from cheap lunch deals to pre-order gig tickets. Pair that with the thousands of Wi-Fi hotspots splattered across the country and O2 is a strong option.

Giffgaff:
Giffgaff proudly claims it is 'the mobile network run by you' but unsurprisingly, you do not run this network, O2 does...sorry to break it to you. Giffgaff calls its SIM plans 'Goodybags' and currently offers some of the strongest offers around. Along with all of Giffgaff's SIMs being 1-month rolling plans, they all also offer some great amounts of data for the price.

ID Mobile:
Carphone Warehouse's very own network, iD Mobile has a few benefits to its name. Most obviously is its cheap pricing. It has the UK's cheapest SIM plan and offers a huge host of low costs. On top of that, all of its plans operate on 1-month rolling contracts meaning you can leave at any time.

Voxi Mobile:
Much like iD above, Voxi gives 1-month rolling contracts. But the thing that really makes Voxi unique is its approach to social media. For Facebook, Whatsapp and a number of other platforms, you will use absolutely no data.

Virgin Mobile:
Virgin offers 12 and 24 month contracts when it comes to SIM only deals. It covers data plans ranging from the cheaper, smaller options through to unlimited data. For those who are existing Virgin customers, you can save some extra money.

Smarty Mobile:
Smarty Mobile is one of the newest members of the world of SIM only deals and yet it remains one of the best options out there. Like Voxi and GiffGaff, it runs on 1-month contracts meaning you can leave at any time. It also offers some of the cheapest prices around.

Lebara:
Lebara is very similar to the above options. It offers 1-month rolling plans and finds its best value at the lower data points, typically getting the best prices around the 2GB data mark. And, with all of its plans, Lebara offers a set number of international calls.

How much data do I need from SIM only deals?

This question is hard to answer and depends completely on how much you use certain apps and features of your phone.

500MB: We'll be honest, unless you almost never use any kind of internet access on your phone, we would advise against going for anything below 1GB. However, if you really won't be using social media, internet or anything else and will just check the occasional email and do a quick Google search, this will be perfect.

1-3GB: With anything in this gap, you'll be able to scroll through social media, browse emails and perform general Google searches. Start pushing into the worlds of streaming, downloads or updates and you'll be hitting your data cap very quickly.

5-10GB: Most people will find that 5-10GB fits their needs perfectly. You can get a bit of Netflix SD streaming in each month, do all of your social media activity and have no fears of going over.

10-30GB: Like to stream TV shows on the train? Maybe download an app on the go? In this sort of remit you'll find that most data intensive services don't affect you too much - as long as you don't do them all the time!

30+GB: At this point, we're getting into the range of not having to worry about how much data you're using. You'll find that you can easily stream HD content, download apps, films and updates without noticing any issues, while still being able to use all of your apps with ease.

Unlimited: It's in the name...no caps whatsoever on your internet usage. When you go unlimited you will have to know that you're already using up your data frequently. If you're currently only using 10-20GB of data...this won't be for you.

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Should I get a SIM or a new phone contract?

It's a hard decision. While a contract takes all of the hard work out for you, it does end up being more expensive in the long-term. If you don't mind forking out a larger sum upfront to pay for a SIM-free phone, you will end up securing the best price this way once combined with a SIM only deal.

However, mobile phone deals offer two major benefits - convenience and a spread of costs. While in most cases you will end up paying more and be stuck in a 24 month contract, you can condense your payments into easier monthly bills and not have to worry about sorting both your phone and SIM plan separately.

Can I keep my old number with a new SIM plan?

Keeping your phone number is a lot easier than it used to be now that 'text to switch' services have been brought out across most retailers. This means you can simply text a number to change numbers across.

You can now send a free text with the word 'PAC' to 65075. Your provider will then have to reply within 1 minute with a PAC code lasting for a whole 30 days. This response will include early termination information and pay-as-you-go fees.

From there you just need to give your PAC code to your new provider. You can now also text 'INFO' to 85075 to get information about your contract. This includes what charges you might need to pay or if you can end your contract early.

You can now also request your new PAC code via your online account with your network. Like the texting option, your network must respond within a minute. If you have more than one number linked to your account (e.g family accounts) you must request your PAC online. 

Contract length: what are my options?

There are three main options in terms of contract length when getting a SIM only deal:

1-month rolling contracts:
These kind of options are great for anyone who's contract has come to an end and is trying to kill time until they get their next one. Or, if you just don't like being trapped in a long contract. There are a surprisingly wide range of great 1-month contracts but the best come from Voxi, Smarty, GiffGaff and iD Mobile.

12 month contracts:
12 months is the length you will see most SIM plans appear on. Some of the best offers, including Three, EE and Vodafone's top offers tend to appear on this contract length and is where most people will end up. 

24 month contracts:
SIM only contracts this long tend to be rare, usually appearing on 12 months instead. However, it is well worth keeping 24 month options in mind as the occasional bargain can sometimes appear.

Do I need unlimited calls and texts with SIM only deals?

Realistically, this isn't something you'll necessarily have to worry about with the majority of plans, most of the SIM deals out there nowadays come automatically with a completely unlimited supply of both calls and texts.

If you find yourself in a plan that doesn't have these included, ask yourself whether you would need it. Do you make lots of calls and texts or do you rely more on your data cap?

Can I get a SIM for my tablet or other device?

In a simple answer - Yes. There are data specific SIMs available for the likes of tablets and computers, allowing you to just pay for data - no calls or texts are included. You can find a collection of these in the comparison chart at the top of the page.

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