Cheapest SIM-Only Deals in the UK: Updated Guide

Why SIM-Only Is Almost Always the Better Deal

If your phone contract has ended or you own your handset outright, switching to a SIM-only plan is one of the simplest and most impactful money-saving moves you can make. The maths is straightforward. Bundled phone contracts spread the cost of the handset across your monthly payments — you are essentially paying off a loan. But once the minimum term ends, you keep paying the same inflated monthly rate even though the phone is fully paid off.

Ofcom data shows that UK consumers overpay by an estimated £182 million per year by staying on expired phone contracts. The average person can save £20 to £30 per month — that is £240 to £360 per year — simply by switching to a SIM-only plan on the same or a better network.

A SIM-only deal gives you the same calls, texts, and data. The only difference is you are not paying for a phone you already own. If your handset still works fine, there is almost no reason to stay on a bundled contract.

MVNOs Explained: Why the Cheapest Deals Are Not on the Big Four

The cheapest SIM-only deals in the UK almost never come from EE, Three, Vodafone, or O2 directly. Instead, they come from MVNOs — Mobile Virtual Network Operators. These are smaller companies that do not own their own masts or infrastructure. Instead, they pay to use one of the four main networks and pass the savings on to you.

The coverage and speeds you get on an MVNO are identical to the parent network because you are literally using the same masts. The only differences are branding, customer service, and sometimes deprioritisation during extremely busy periods (though this is rarely noticeable in practice).

Here is which MVNO runs on which network:

EE network: BT Mobile, Plusnet Mobile
Three network: Smarty, iD Mobile, Superdrug Mobile
Vodafone network: VOXI, Lebara, Asda Mobile, Talkmobile
O2 network: Giffgaff, Tesco Mobile, Sky Mobile, Lycamobile

Knowing the parent network matters because it determines your coverage. If Three has poor signal in your area, any MVNO running on Three will have the same issue.

Best Deals by Data Tier

Ultra-Budget: 1GB to 5GB (£3 to £6 per month)

If you are mostly on Wi-Fi and use your phone for calls, texts, and light browsing, you do not need much data at all. These plans are ideal for older family members, children, or anyone who is almost always connected to Wi-Fi.

Smarty 1GB: Around £3 per month, rolling monthly contract, Three network. Smarty also refunds unused data, so if you use even less than 1GB, you pay even less.
Lebara 5GB: Around £5 per month, Vodafone network. Includes 100 international minutes to selected countries, making it excellent for people who call family abroad.
Giffgaff 5GB: Around £6 per month, O2 network. Giffgaff operates on a "goodybag" system — 30-day rolling plans with no contract.
iD Mobile 5GB: Often available for under £5 per month on short promotional deals, Three network.

Mid-Range: 10GB to 30GB (£6 to £10 per month)

This is the sweet spot for most people. Enough data for regular social media, streaming music, maps, and moderate video watching on the go.

Smarty 30GB: Around £8 per month, rolling monthly, Three network. Outstanding value.
Lebara 15GB: Around £7 per month, Vodafone network. Again includes international minutes.
iD Mobile 25GB: Frequently on offer for around £7 to £8 per month, Three network.
Giffgaff 15GB: Around £8 per month, O2 network.
VOXI 15GB: Around £10 per month, Vodafone network. Includes unlimited social media data — meaning usage on apps like Instagram, TikTok, WhatsApp, Snapchat, and Facebook does not count towards your allowance.

Heavy Use: 50GB to 100GB (£8 to £12 per month)

For people who stream video on the go, use their phone as a hotspot, or simply do not want to worry about running out.

iD Mobile 100GB: Regularly available for under £10 per month, Three network. This is often the single best value deal in the UK market.
Smarty 50GB: Around £10 per month, rolling monthly, Three network.
Lebara 100GB: Around £10 per month, Vodafone network.
Three 100GB (direct): Around £12 per month, sometimes less on promotional deals. Includes Three's Price Lock — your price will not increase for the duration of your plan.

Unlimited Data (£10 to £20 per month)

If you use your phone as a primary internet device, hotspot regularly, or simply never want to think about data limits.

Smarty Unlimited: Around £12 per month, rolling monthly, Three network. No speed caps, no fair usage limit in practice. This is arguably the best unlimited deal in the UK.
Three Unlimited: Around £14 to £17 per month depending on the contract length. Includes 5G at no extra cost.
VOXI Unlimited: Around £15 per month, Vodafone network. Includes unlimited social media and video streaming data.
iD Mobile Unlimited: Around £14 per month, Three network.
Giffgaff Unlimited: Around £15 per month, O2 network.

For comparison, EE and Vodafone charge £20 to £30 per month for their own-brand unlimited plans. You are paying a premium for the brand name and customer service, not for better coverage.

Contract vs Rolling Monthly

SIM-only deals come in two flavours: fixed-term contracts (usually 12 or 24 months) and rolling monthly plans (cancel anytime with 30 days' notice).

Fixed-term contracts are typically £1 to £3 per month cheaper than equivalent rolling plans. The trade-off is that you are locked in. If a better deal appears six months later, you cannot switch without paying an early termination fee.

Rolling monthly plans cost slightly more but give you complete flexibility. You can switch provider every single month if you want. For most people, this flexibility is worth the small premium — the SIM-only market moves fast, and better deals appear regularly.

Our recommendation: Unless the fixed-term price is dramatically cheaper, go rolling monthly. The ability to switch at any time means you can always jump on the latest deal.

How to Switch Without Losing Your Number

Switching your mobile number to a new provider has never been easier in the UK, thanks to Ofcom regulations. Here is the process step by step:

Step 1: Get Your PAC Code

Text PAC to 65075 from the phone with the number you want to keep. You will receive your Porting Authorisation Code within 60 seconds by text message. This code is valid for 30 days.

A PAC code tells your old provider that you are leaving and want to take your number with you. By law, they must provide it immediately upon request — they cannot refuse or delay.

Step 2: Give the PAC to Your New Provider

When you sign up for your new SIM-only deal, enter your PAC code during the activation process. Most providers have a field for this on their website or app.

Step 3: Wait for the Port

Your number will transfer to your new SIM within one working day of the port being initiated. During the switch, you will be without service for a brief period — usually one to three hours. Your old contract is automatically cancelled as part of the porting process.

What If You Do NOT Want to Keep Your Number?

If you want a fresh start with a new number, text STAC to 65075 instead. This gives you a Service Termination Authorisation Code, which cancels your old contract without porting your number.

eSIM: The Future of SIM-Only

An increasing number of UK providers now support eSIM — an embedded SIM that is built into your phone and activated digitally. No physical SIM card needed, no waiting for delivery.

Providers currently offering eSIM in the UK include:

EE, Three, Vodafone, O2 (all four main networks)
Giffgaff, VOXI, Smarty (selected MVNOs)

eSIM is particularly useful if you want to use two numbers on one phone — for example, a personal and work number, or a UK number and an international number for travel. Most modern iPhones and Samsung Galaxy devices support eSIM.

5G: Do You Actually Need It?

Providers love to upsell 5G, but here is the honest assessment for most UK users: you probably do not need it yet.

5G coverage in the UK is still concentrated in city centres and major towns. If you live in a rural area or spend most of your time outside urban zones, you will be on 4G most of the time regardless of what your plan says. Ofcom's 2024 coverage data shows that 5G is available to approximately 50 percent of UK premises from at least one provider, but actual street-level coverage is patchier.

That said, 5G is increasingly included at no extra cost on many SIM-only plans, particularly from Three and VOXI. If your plan includes 5G for free and your phone supports it, great — you will benefit in areas with coverage. But do not pay a premium for 5G access unless you are in a well-covered area and regularly need the fastest possible mobile speeds.

To check 5G availability at your location, use the coverage checkers on each network's website:

EE: coverage.three.co.uk (note: this is Three's, for EE use coverage.three.co.uk — actually use each provider's own checker)
Three: three.co.uk/coverage
Vodafone: vodafone.co.uk/network/status-checker
O2: o2.co.uk/coveragechecker

Roaming: What Is Included?

Since Brexit, free EU roaming is no longer guaranteed by UK law. Each provider sets its own roaming policy:

Three: Includes roaming in 71 destinations at no extra cost on most plans (Go Roam)
Smarty: No free roaming — you pay per MB/minute/text abroad
Giffgaff: Includes EU roaming on most goodybags at no extra cost
VOXI: Includes EU roaming in your allowance
Lebara: Includes roaming in 50+ countries on selected plans
iD Mobile: Includes EU roaming on selected plans
EE: Charges a daily roaming fee of £2.47 in Europe on newer plans

If you travel to Europe regularly, roaming policy should be a significant factor in your decision. Three and Giffgaff offer the best roaming value among budget providers.

When to Buy: Seasonal Deals

SIM-only prices fluctuate throughout the year. The best times to grab a deal are:

Black Friday and Cyber Monday (late November): The single best time to buy. Providers slash prices aggressively, and you can often find 100GB plans for under £8 per month.
Boxing Day and January sales: Another strong period, particularly for rolling monthly deals.
Back to school (September): Providers compete for student sign-ups, and the deals often apply to everyone.
Mid-contract price rise season (April to May): After the annual price increases, providers try to attract switchers with competitive new-customer deals.

If you are on a rolling monthly plan, there is nothing stopping you from switching every time a better deal appears. Set a reminder to check prices every few months.

Three's Price Lock Promise

Three is the only major UK network that offers a Price Lock guarantee — meaning the price you sign up at will not increase for the entire duration of your plan. Every other major provider reserves the right to raise prices mid-contract, typically by CPI plus 3.9 percent each April.

This makes Three (and its MVNOs like Smarty and iD Mobile) particularly attractive if you want cost certainty. However, note that Smarty's rolling monthly plans already give you protection because you can leave at any time — if Smarty raised prices, you could simply switch to another provider the next month.

The Bottom Line: How Much Should You Be Paying?

Here is a rough benchmark for what you should be paying on a SIM-only plan in the UK:

Light user (under 5GB): £3 to £6 per month
Average user (10 to 30GB): £6 to £10 per month
Heavy user (50 to 100GB): £8 to £12 per month
Unlimited data: £10 to £15 per month

If you are paying more than these ranges, you are almost certainly overpaying. The SIM-only market is fiercely competitive, and there is no reason to pay a premium unless you specifically want the customer service and brand experience of a major network.

The simplest action you can take today: text PAC to 65075, compare deals on a site like Uswitch or Money Saving Expert, and switch. The whole process takes less than ten minutes of active effort, and you will likely save £100 to £300 per year. That is real money back in your pocket every single month.