Mobile SIM Buying Guide
I've helped a lot of customers save money on their mobile phone bills. The trick isn't simply to find the cheapest SIM card. The trick is to find the cheapest useful SIM card on the network that actually works where you live.
What's a Virtual Network?
We have four main mobile networks in the UK: Vodafone, O2, Three and EE. They operate the mobile network infrastructure that your phone connects to.
Alongside them are lots of smaller companies known as virtual network providers, or MVNOs. You may already have heard of companies such as giffgaff, SMARTY, Tesco Mobile, Lebara and Talkmobile.
These companies don't need to build a complete mobile network of their own. Instead, they buy access from one of the four main networks and resell the service to their own customers.
Because many virtual providers don't have large high-street shop networks, enormous advertising budgets or traditional telephone support centres, they can often charge considerably less.
The important bit is that the mobile signal comes from the same underlying network. For example, Lebara and Talkmobile use Vodafone, while giffgaff uses O2. So if Vodafone gives you good coverage, a Vodafone-based virtual provider can give you that network coverage without necessarily charging Vodafone's own prices.
How I Help Customers Choose
I've helped many customers find a better mobile deal, and I always do it in the same order.
Choose the network
Find out whether Vodafone, O2, Three or EE gives you the best signal where you actually use your phone.
Choose your data
Work out roughly how much mobile data you need. For many people, 20GB to 30GB is more than enough.
Choose the deal
Pick from the cheapest option, a sensible everyday option, or unlimited data.
Network First. Price Second.
Most people already have some idea which networks work well where they live. Customers often say things to me like, "O2 is terrible here, we're all on EE" or "Vodafone's the only one we can get a decent signal on in our village."
That's the first decision. There is absolutely no point saving a couple of pounds a month on a SIM card if you can't make a call or send a WhatsApp message.
Don't know which network is best where you live?
Get in touch with me and I'll help you work it out. Call or message me on 07704 33 22 23.
How Much Data Do You Actually Need?
Once you know which network you want, the next question is how much data you need.
Almost every SIM plan now includes plenty of calls and texts, so the main difference between plans is usually the amount of mobile data included each month.
What does GB mean?
Mobile data is measured in gigabytes, usually shortened to GB or simply called "gigs".
As a very rough guide, 1GB could be around an hour of HD video streaming or many hours of listening to music online. The exact amount varies depending on the app and the quality settings you use.
You'll see SIM cards advertising 50GB, 80GB, 100GB or even 150GB. Those numbers look impressive, but bigger isn't automatically better. If you only use 10GB each month, paying extra for 100GB doesn't make your phone work any better.
For many everyday users, 20GB to 30GB is a very comfortable allowance. That's why I use that sort of plan as the mid-range choice below.
Why Only Three SIMs for Each Network?
There are hundreds of SIM deals and I don't think giving you hundreds of choices is particularly helpful.
I've researched the virtual providers that use each of the four networks and picked three straightforward choices:
Cheapest
The lowest-cost usable monthly SIM I can find for someone who just wants the basics.
Mid Range
A low-cost plan with at least 20GB of data. This is the type of SIM I recommend for most people.
Unlimited
For heavy data users, or anyone who simply doesn't want to think about how much data they're using.
Choose Your Network
Find the network that gives you the best signal, then choose the SIM that best suits the way you use your phone.
Vodafone Network
These SIMs all use the Vodafone mobile network.
O2 Network
These SIMs all use the O2 mobile network.
Three Network
These SIMs all use the Three mobile network.
EE Network
These SIMs all use the EE mobile network.
Last checked: 21 August 2026
Prices and allowances were correct when this page was last updated. Mobile providers can change their plans, prices and terms, so please check the provider's website before ordering.