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The best SIM only deals in September 2021

SIM only deals offer an affordable and flexible way of getting a brand new SIM card. Saving you from the long contracts of a full phone contract, SIM cards on their own continue to grow in popularity.

Of course, a straight up phone contract is easy. But the ease of it means you end up chucking a fair bit of extra money away each month. Do a bit of searching and SIM plans could supply you with low costs, 1-month flexible contracts or an unlimited data cap way below what it should really cost.

SIM only deals comparison:

The sheer variety of SIM only deals available has broadened over the years with new networks entering the market, the introduction of 5G SIMs, and plenty of competition that all helps to drive your costs way down. No longer is it just the usual names of EE, O2, Three and Vodafone - there's a wide range of options to choose from.

Cheap SIM providers like iD Mobile, Smarty and Lebara can keep your costs low - perfect for cheap SIM-free phones. Three, EE and Vodafone SIMs can shower you in data. While Voxi and GiffGaff are among those that can supply you with 1-month rolling contracts allowing you to leave at any time. Along with value, flexibility is the name of the game when you go SIM only.

If you already know you want a SIM plan and even know the data cap, network and more, then this should be easy! Simply use our SIM comparison chart above to find your perfect option.

Entering a daunting new world? Want to know what a SIM is and what it stores? Or just not sure what you really need? That's where we step in with a complete guide below to get you set up!

What is the best SIM only deal?

There is no obvious answer to this question and it will very much depend on what exactly you need from a new SIM plan. However, there are a few choices that do stand out.

Three SIM only deals are often the best value. For example, it currently offers unlimited data for just £16 a month- the UK's cheapest ever 5G unlimited data SIM. Or EE - the UK's most popular network - can supply 160GB for £20 a month.

For some, the best SIM plan will remain flexible with 1-month rolling contracts. For those people, Smarty's 30GB for £10 a month offer or Voxi's 12GB for £12 a month with unlimited social media and streaming usage are obvious choices.

Realistically, each network has its own selling point, these are:

  • Three: best for big data and unlimited plans
  • EE: best for fast speeds and overall performance
  • Vodafone: strong balance of affordability and features
  • O2: heavy on the added benefits
  • Smarty Mobile: best value 1-month rolling options
  • Voxi: best for social media users
  • Lebara: best for cheap plans that include international minutes
  • BT Mobile: best existing customer discounts

SIM only deals: top 5 this week

1. Best SIM overall:

Three SIM | 12-month contract | All-you-can-eat data | Unlimited calls and texts | £16 per month
Right now, this is the best SIM plan on the market for overall value. Three is currently offering a completely unlimited data, calls and texts plan while only charging you £16 a month. That's the cheapest price on the market for unlimited data and with Three, you'll get 5G at no extra cost.
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2. Best 30-day SIM plan

Smarty SIM | 1-month contract | 50GB data | Unlimited calls and texts | £15 £12 per month
Smarty operates all of its SIM plans on 1-month rolling contracts making it a fantastic flexible option. Right now, the best value option from Smarty is this 50GB offer. It will only cost you £12 a month which is the overall cheapest price on the market for this much data.
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3.  Best EE SIM only deal

EE | 24-month contract | 120GB data | Unlimited calls & texts | 5G ready | £20/pm
EE is often one of the priciest networks around but if you're after it for its position as the UK's fastest and most popular network, this will be the deal for you. It only costs £20 a month but for that price, you'll get an impressive 120GB of data. That's plenty of data for gaming, streaming and plenty more.
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4. Best Vodafone SIM

Vodafone SIM | 12-month contract | 100GB data | Unlimited texts and calls | £16 per month + £40 cashback
This offer from is going to be the best Vodafone SIM for most people. It only costs £16 a month but for that price you'll secure 100GB of data. On top of that, this plan also comes with £40 in cashback which effectively leaves you paying just £12.67 a month for this deal.
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5. The best cheap SIM plan

SIM only plan from Lebara | 1-month contract | 2GB data | 1000 minutes and texts | £2.50 a month for first 3
If you're simply after the UK's cheapest SIM plan, Lebara is the way to go. The network has a £5 a month SIM plan that secures you a pretty decent 2GB of data. While that alone is a market-leading price, use the code TECH21 at the checkout and you'll only pay £2.50 a month for the first 3 months of your contract. On top of that, Lebara is a flexible network, allowing you to leave at any time - even after the 3 months discount is up.
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How does a SIM only deal work?

SIM card

(Image credit: Daniel Kaesler / EyeEm)

What does a SIM card do and what's stored on one?

A SIM card has a couple of purposes. Most importantly, it is used to identify the phone contract you've signed up for, fulfilling your data, calls and texts plan.

A SIM plan also provides two numbers with overly complicated names -  the ICCID serial number, International Mobile Subscriber Identity number (IMSI) and the Mobile Subscriber Integrated Services Digital Network number (MSISDN), the later of which is the user's telephone number.

In other words, a SIM card identifies your phone number and the SIM plan that you've subscribed to. Read our full SIM card storage guide to find out more.

What does SIM stand for?

As is usual for popular pieces of tech, SIM stands for something that sounds complicated but is quite simple. SIM stands for 'Subscriber Identity Module' - another way of saying a device to identify your phone deal. 

Why get a SIM only deal?

There is a lot of benefits to choosing a SIM tariff over a phone contract. While it can be slightly more complicated especially if you need a new phone as well, its flexibility, affordability and other factors help make it an obvious choice.
When you break down the costs of a phone contract, you realise that you're paying a lot more than simply buying the phone and SIM separately. A SIM plan alone will be much cheaper, even if you're having to buy a new phone with it.

A phone contract will always tie you in for a minimum of two years so you can pay off your costs. However, a SIM plan can be anywhere from just 1 month long, allowing you to sell off your phone if it breaks or you decide you want something new.

With such a wide variety of prices, data caps and networks, choosing a SIM plan allows you to customise your plan to the exact factors you want. This is especially helpful if you have your eyes on a network that doesn't sell phone contracts.

Phone contracts end and if you decide your happy with your handset, why hand it in for something new? If you're more than happy with the handset you have, hold on to it and get a cheaper SIM, allowing you to enjoy that handset for longer.

Picking the right SIM:

SIM card in smartphone

(Image credit: Nerosu)

There's a surprisingly large amount of factors to consider when choosing a SIM plan and while there aren't really any bad choices, it's about working out what factors suit your needs.

Do you want the fastest option with no concern for price? EE is the choice to go for. Need a rolling 1-month contract? Voxi, Smarty, GiffGaff and more are available. Or do you just want a cheap SIM?

How much should you be paying for a SIM only deal?

SIM prices vary massively between networks and data caps and knowing how much to pay will depend on this. If you're not too worried about the network you're with and need next to no data, you can keep your bills to around £5-£8 a month.

However, going for EE SIM only deals - the UK's fastest and most popular network - will mean paying a fair bit more than the competition, often exceeding £20 a month. Decide how much data you require and consult your options based around that, considering both price and your preferred network.

How much data do you need?

While almost every single SIM plan will automatically offer unlimited texts and calls, data caps can range massively from 500Mb all the way through to unlimited data SIM only deals.

There are plenty of options in excess of 30GB, but the large majority of people are unlikely to need this much, usually using under 10GB each month. The easiest way to decide how much data you need is simply to consider how much you'd previously used on older contracts.

First time you're getting a SIM? These are how the data caps line up with usage:

  • 1GB: A limited option that won't be enough for most. If you rarely use the internet and occasionally need to use Google Maps or check the internet, this can be a cheap option.
  • 5GB-10GB: This is the range most people will fit into. It allows for pretty intensive usage of social media, Maps and internet searches without fear of running over. While you can do a bit of streaming, don't push it and avoid HD!
  • 10GB-50GB: If you like to stream when you're out and about, use maps on a daily basis and generally have a data intensive lifestyle, this will likely be a cap you should be looking in. Keeping under 50GB can keep your costs at a still affordable point.
  • 50-100GB: At this point, you're going to have to be a real data drainer for this to be necessary. Downloading apps on the go, HD streaming, big downloads and working from home.
  • 100GB-unlimited: Unlimited data plans have significantly come down in price over the years and can even be a legitimate alternative solution to having full broadband if you live somewhere with an excellent 4G/5G connection. However, for most people, it's not going to be necessary.

What contract lengths are available?

There are four types of contract lengths available with SIM only deals - 1-month rolling, 12 months, 18 and 24. Realistically, 18-month contracts are pretty rare so the other three are the ones you'll see more.

24-month contracts tend to be the cheapest per month on big data plans but you're tied in for a while. 1-month rolling plans from the likes of GiffGaff, Voxi and Smarty are surprisingly affordable but you won't find them with the four main networks.

12-month contracts are the tariffs that come up most often and for the majority of people, will be the best choice.

EEO2ThreeVodafoneVoxiGiffgaffSmartyBTLebaraVirginiD MobileSky
Contract lengths:12 or 24 months1, 12 or 18 months1, 12 or 24 months1, 12 or 24 months1-month rolling 1-month rolling1-month rolling12 or 24 months1-month rolling12 or 24 months1-month rolling12 months
Best price point:60GB+Up to 10GBUnlimited data60GB+1-month rolling1-month rolling30-50GB20GB2GB30-50GB2-12GB10GB
5G enabled?YesYesYesYesYesYesNoYesNoYesNoYes
Unique features:UK's fastest networkFree Disney Plus + O2 Priorities Cheapest unlimited SIMVeryMe rewards schemeUnlimited social mediaPayback + free texts to Giffgaff customersData rollover + money back on dataExisting customer discountsInternational minutesData-free Whatsapp, Twitter and Facebook messagesData rolloverData rollover
Unlimited calls and texts?YesYesYesYesYesYesYesYesOn select plansYesOn select plansYes

What incentives and special features do SIM only deals have?

Obviously factors like data caps, contract lengths and price are the key factors you should focus on, but each network has a number of interesting special features to make them stand out.

Unique features:

Voxi for example won't use up any of your data while you use social media apps like Facebook, Whatsapp, Twitter, Instagram and more. EE offers free subscriptions to popular services, Vodafone and O2 have their reward schemes - VeryMe and O2 Priorities - and most other networks have similar options.


A lot of SIM only deals will also come packed with cashback, giving you money back with your plan. This can significantly reduce your overall costs. This can come in the form of automatic cashback or cashback by redemption.

While cashback by redemption is the option that will save you more money, it is more complicated to deal with. Automatic cashback is a lot simpler, giving you all of your money back in one easy payment. 

Slightly more rare, SIM plans can occasionally come with a free gift. These could be smart tech like speakers, TVs or tablets. We've seen everything from headphones through to smartwatches.

Of course, these aren't all that common and you need to be wary of a SIM plan that is offering a gift...but has included the price of the gift in your monthly bills.

What SIM card size do I need?

SIM cards these days fall into three sizes and these are: Standard, Micro and Nano, descending in size. More on eSIMs below. If you're ordering your SIM only you'll likely find it arrives in a credit card sized piece of plastic out of which can you pop your microchip SIM.

A standard SIM measures 25 x 15mm and was used in phones before 2010 and a few after then.

The Micro SIM stands at 15 x 12 mm and was used in phones from 2010 and you'll still find some phones work with these now.

The Nano SIM, introduced in 2012, measures in at 12.3x 8.8mm and is the most commonly used SIM in phones.

The Combi SIM might be what you get sent by a SIM only provider as it contains all three sizes, and you push out the one that fits your phone. This is ideal as you don't need to know your size prior to this as you can hold it up to the SIM tray and see.

How to switch to a new SIM only deal:

Three SIM cards stood up

(Image credit: Passakorn Leelawat / EyeEm)

How to switch SIM plans:

Switching phone plans has become a much easier process than it was in the past. Where before you had to go back and forth between your old and new provider, gathering details, now it's just a few steps.

Firstly, you need to know you're eligible to switch plans. If your contract still has a few months until it ends, you are likely to be charged for the remaining time meaning it is usually best to fully finish your contract first.

Switching and keeping your number:

Once you know when your contract is finishing and you've got your new deal, you need to decide if you want to keep your number. If so, you can request a PAC code (Porting Authorisation Code) from your old network. This can be done via the phone or through a text.

Then you simply get in touch with your new provider and give them your new code. Each phone number or text code to get a PAC code is different for each network - all of them list this information clearly on their websites.

Switching with a new number:

Don't want to keep your number - it's even easier! Simply get in contact with your new provider and tell them you want a new number and tell your old network your ending your contract.

This can also be done via a text to switch service. Simply text STAC to 75075.

Will my phone be locked to a network?

If you're looking to get a new SIM plan for an old phone - whether its yours or one you bought secondhand - you could find that it is locked to a network. This is where a phone has had a SIM in it and now can only use that network.

While that sounds permanent, it's actually easily fixed. First, try putting a SIM card from another provider into your phone. Make a call and if you can't then its locked. You can also get in contact with your network to find out if its still locked.

How to unlock a smartphone:
Unlocking a smartphone is either a breeze or a bit more complicated depending on the network its locked to:

  • EE Once six months have gone by on your contract, you can call EE on 0800 956 6000 and pay them £8.99 to unlock your phone. It says it will take around 10 days to complete. PAYG phones can be unlocked for free. Both iPhones and Google devices unlock for free after a certain time with EE.
  • O2 Whether you have an iPhone or Android device, pay as you go or on a contract, O2 can unlock it for free. You simply need to log into the O2 app, select unlock my phone and you're good to go.
  • Three Fear not, all phones on Three are unlocked as standard. Shove whatever SIM you like in there, it will work a treat.
  • Vodafone The red network doesn't quite get the same marks as Three, as your phone will be locked to them on arrival. But they have made unlocking handsets absolutely free within 10 days of your request.

SIM networks: MVNOS and main carriers:

Over the years, a massive range of networks have emerged now resulting in a lot of choice. However, there are four main networks that support all of these other options.

EE, O2, Three and Vodafone are the four main networks. The factor that makes them stand out is that they use their own service, coverage and reach across the UK, all of the rest of the networks 'piggyback' off of these four.

Piggybacking, while a strange term to use, simply means a network makes use of one of those four main network's coverage. Virgin and Voxi use Vodafone's coverage, iD Mobile and Smarty uses Three's and GiffGaff and Sky use O2s.

These networks are referred to as MVNOs (Mobile Virtual Network Operator). Using one of these piggybacking networks doesn't mean you'll get a weaker connection or any worse coverage than the main options. It's exactly the same as being on the original network...just you won't get access to their additional features like reward schemes or EE's free subscriptions.

Networks and piggybacking
EEO2ThreeVodafoneVoxiSmartyBTLebara VirginiD MobileSkyGiffgaff
Does it have its own network?YesYesYesYesNoNoNoNoNoNoNoNo
What network does it use?EEO2ThreeVodafoneVodafoneThreeEEVodafoneVodafoneThreeO2O2
Alex Hughes

As the editor of all things broadband, SIMs and phone contracts, Alex is constantly scouring the internet to land you the best prices. Whether that be with the latest iPhones, breaking down how broadband works or revealing the cheapest SIM plans, he's got the know.