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How do SIM-only plans work?

Richard Murphy
Thursday, March 24th 2016

In the old days there was little choice but to go to a shop and choose a new handset locked to a specific network.

We live in a different world now. One where if your existing handset is still bursting with life, you can pretty much switch tariffs willy-nilly – every month or every year – it’s up to you. That’s the beauty of SIM-only deals, and here’s how they work...

A SIM-only plan is a new deal for your existing handset

If you’ve got a phone you’re happy with, and want to avoid the expense of a new one, you need a SIM-only plan – a SIM on its own with no handset attached.

Physically, SIMs come in three different sizes: standard, micro and nano, but it’s not their physicality that sets them apart from one another, rather the balance of calls, texts, data (internet), international calling, roaming discounts and so on to be found within each.

Most of the main providers offer a wide variety of SIMs, each a cocktail of these various elements. It's a good idea to know exactly what you intend to use the SIM for before making your final choice.


  • SIM-only plans are usually cheaper than getting a contract with a handset
  • SIM-only plans usually offer a wider array of contract lengths than traditional phone and SIM plans


  • You won’t get a new phone, so be sure your existing one has plenty of life left in it
  • Your phone might need to be unlocked before you can use a SIM from another provider in it

Types of SIM-only plan

There are two different ways to go – pay monthly, or pay-as-you-go (PAYG). Both have benefits and drawbacks. There are also special data-only SIMs with no calling plan – these are designed specifically for tablets such as Apple’s iPad.

Pay monthly plans

Pay monthly SIM-only plans come with a monthly allowance of minutes, texts and data for a set monthly price. Most providers have a decent number of pay monthly SIMs to choose from, so you can find the right one for your usage and pocket.

One drawback to a pay monthly SIM-only contract is that, well, it’s a contract, and you’ll be punished if you need to break its terms. Most pay monthly contracts last 12-months, but there are 1-month rolling contracts that usually cost a little bit more.

Pay-as-you-go plans

With PAYG you ‘top up’ your phone’s balance when you need to and only pay for what you use.

Some providers offer additional minutes, texts and data if you top up by a set amount over the course of a month to thank you for your loyalty.

Data-only plans

If you want to get your tablet computer online when out of wi-fi range, you’ll need a data-only SIM. That is, a SIM with no phone number, texts minutes or any phone-related guff.

The majority of data-only SIMs are pay monthly, but there are some PAYG deals around too.

Which providers offer SIM-only deals?

There are four physical mobile networks in the UK – EE, O2, Vodafone and Three.

Other mobile providers like Virgin Mobile, giffgaff and TalkTalk and many, many others are what's called ‘mobile virtual network operators’ (or MVNOs).

They rent network resource from the four physical network owners, so their coverage and data speed is comparable to that of the network carrier, while offering their own unique deals.

EE has the widest coverage and fastest 4G

EE has both pay monthly and PAYG SIM deals. Its pay monthly plans come with either 12-month or 30-day contracts and there’s a variety of different PAYG ‘packs’ which give you a combination of data, texts and minutes for a set price.

It also has data-only SIM deals, so you can harness EE’s extremely quick 4G network.

EE has both the fastest and largest 4G network in the UK. In its most recent report Ofcom clocked EE’s average 4G speed as 33Mbps, covering 99% of all UK premises.

Those of you living in London might also be able to take advantage of EE’s double-speed 4G which, so EE claims, can reach speeds of up to 90Mbps.

O2 has free public wi-fi

Like EE, O2 has a variety of 12-month and 30-day pay monthly SIM deals, each with various combinations of texts, minutes and data limits, and all with access to O2’s 4G network. It also offers Pay & Go SIMs (O2-speak for PAYG).

Joining O2 gives you free access to wi-fi in thousands of public spaces including bars and shops. You’ll also be eligible for early access to event and gig tickets with O2 Priority. Fancy.

O2 has the third-fastest 4G network with an average speed of 33Mbps according to Ofcom. It has the second-widest network, however, with 97% of UK premises covered.

Vodafone offers appealing entertainment extras

Vodafone has both pay monthly and PAYG SIMs on both 12-month and 30-day contracts and offers 4G as standard wherever coverage is available.

Vodafone’s 4G network is rather good. It sits just behind EE’s network in terms of speed, with Ofcom measuring it as having a 20Mbps download speed on average. Vodafone 4G currently covers around 95% of UK premises.

A nice feature that Vodafone offers is free access to popular digital services like Now TV, Spotify, Netflix or the Sky Sports Mobile TV app for a limited period on some of its SIM deals.

Three is the only ‘unlimited data’ network provider

Three has pay monthly and PAYG SIMs both for phones and for tablets. Three is the only provider of the four network holders that offers unlimited data, even on its 4G network. Which is great news if you’ve got a bottomless capacity for data, right?

Well, it’s not quite as great as it sounds. Three came at the bottom of the pile in the most recent Ofcom tests for average 4G speed and UK coverage. It came in at 17Mbps and covers 91% of UK premises.

On the bright side Three’s network is the most reliable, and it allows you access to its 4G network regardless of what plan you’re on. Three customers can also use their phones abroad at no extra cost in selected countries.

Everyone else

With less physical infrastructure to support, savings can be made by going with a provider other than the big four. This is a list of our favourites, along with the network on which they run.

  • Giffgaff (O2)
  • Tesco Mobile (O2)
  • Lebara Mobile (Vodafone)
  • TalkTalk Mobile (Vodafone)
  • iD Mobile (Three)
  • Asda Mobile (EE)
  • BT Mobile (EE)
  • The People’s Operator (EE)
  • The Phone Co-op (EE)
  • Virgin Mobile (EE)

Where can I compare SIM-only plans?

Our Ofcom-approved SIM comparison tools allow you to compare by provider, monthly cost, contract length and text, voice and data allowances. Happy hunting!

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