A SIM, which stands for ‘subscriber identity module’, is the small plastic card provided by your network that slots inside your mobile phone. It holds information, such as your mobile number, and allows you to make and receive calls and texts, and use data on your phone.
Without a SIM, you won’t be able to access your network and use your phone (although a handful of the latest phones now work using e-SIMS).
SIMs make it easy to swap handsets. If you take your SIM out of your handset and put it into another one, you’ll be able to make and receive calls and use data on the new phone (assuming it is unlocked).
Likewise, you can put a new SIM into your existing handset and make calls on a different number or different network.
What is a SIM-only mobile tariff?
Traditionally most mobile phone tariffs had two elements: a new handset and an airtime plan (the cost of your data, minutes and texts), and both were bundled into one monthly price. The handset was often described as ‘free’ – but it wasn’t really, you simply paid for it over the course of the contract.
SIM-only mobile plans just come with a SIM, not a handset. You can either buy a handset separately, or put the SIM into a handset you already own.
You might opt for a SIM-only tariff because you:
- want to keep using your existing handset when your contract ends
- want to buy a particular handset outright
- already own a handset you want to use
- want to save money
- have a poor credit history and so aren’t eligible for a bundled deal
Which providers offer SIM-only deals?
All the main networks – O2, Three, Vodafone and EE – offer SIM-only deals.
But there are lots of other options too. These come from operators who ‘piggyback’ off the main networks.
Other mobile firms offering SIM-only deals include BT, Sky, ID Mobile, GiffGaff, Plusnet, Smarty, Voxi, and Tesco Mobile.
Some firms also offer 5G SIM-only deals. 5G is the next generation of mobile technology and offers super-fast speeds. You’ll need a 5G-enabled handset and to live in an area covered by 5G, to benefit from a 5G SIM-only deal.
You can compare SIM-only deals here.
Can I keep my phone number?
Yes, you can keep your number when switching to a SIM-only deal.
If you’re staying with the same network, it will be able to send you a new SIM for activation on the same number.
If you’re switching networks, you’ll need to get a PAC (Porting Authorisation Code) from your existing network and give it to your new network which will arrange the switchover.
Types of SIM-only deal
You can get a SIM-only deal on a 12-month, 18-month or 24-month contract. This will give you a SIM and a set amount of call minutes, texts and data each month. These deals tend to work out the cheapest, especially if you pick a longer contract term.
If you want more flexibility, you can get a 30-day SIM deal, which means you’re only committed for a month.
If you don’t use your phone much, a pay-as-you-go SIM can be topped up with credit, and then you pay a set amount per call minute, text or GB of data.
Some internet-enabled devices such as tablets and iPads have a SIM card slot in the same way your smartphone does. A data-only SIM connects these devices to the internet via the mobile network.
What is an unlocked handset?
There’s one tricky factor when you opt for a SIM-only mobile tariff: you need an unlocked handset.
In most cases when you buy a handset as part of a bundle or contract, it will be ‘locked’ to a particular network.
This means if you insert a SIM from a different network into your phone, it won’t work. Networks lock handsets in an attempt to make it difficult for you to switch to a different network.
But not all handsets are sold as locked. In fact, from December 2021 UK mobile firms will be banned from selling locked handsets.
Until then, you’ll need to get a locked handset unlocked in order to use a SIM from a different network. You can unlock a handset in two ways:
- call your network and ask it to unlock it
- go to an independent phone shop and ask for your handset to be unlocked
Both options will cost about £10 to £15.
Have I got the right-sized SIM?
SIMs come in three sizes:
A smartphone will have a SIM slot that’s one of these sizes and you’ll need to have a SIM that fits your phone.
However, it’s not as complicated as it might seem as, these days, almost all smartphones have a nano SIM slot.
Some of the latest smartphones don’t have a plastic SIM at all, but an eSIM instead. You can read about eSIMs in this guide.
Are SIM-only plans cheaper than bundled contracts?
SIM-only mobile plans are much cheaper than deals including a handset because the network doesn’t have to provide the handset.
Some SIM-only deals are just £5 or £6 a month.
However, obviously you will need to provide the handset yourself. You might buy a new one or use one you already own.
In many cases buying a new handset outright and pairing it with a SIM-only deal can work out cheaper than buying the handset together with an airtime plan. It also means you can upgrade the handset when you want without tinkering with the airtime plan, or vice versa.
However, buying a handset separately means you’ll need to have the cash to spend upfront in one go, opposed to a bundled contract where you can effectively pay for the handset in monthly instalments.