Best UK SIM-Only Deals

What is a SIM-only plan?

A SIM-only plan is just airtime - calls, texts and mobile data delivered through a SIM card you slot into a phone you already own. There is no handset bundled in, no upfront device cost, and no 24-month finance commitment. You pay only for the network service, which keeps your monthly bill noticeably lower than an equivalent contract that includes a phone. Plans range from rolling 30-day deals you can cancel any time, up to 12-month fixed terms with bigger data allowances. The right plan depends on three things: how much data you actually use, how much flexibility you need, and which network has the best coverage at your home and work postcodes.

What is included in a SIM-only plan

Every SIM-only plan includes a monthly allowance for three things: data measured in gigabytes, voice minutes, and SMS texts. Most plans also include free use of your allowance across the EU within fair-use limits, though Lebara is a notable exception - see our EU roaming SIMs page for plans that travel without surcharges. The big four networks (EE, O2, Three, Vodafone) bundle in extra perks - free streaming subscriptions, swappable benefits, priority access to events - that the cheaper MVNOs do not. If you do not value those perks, an MVNO running on the same network masts will usually undercut the host on price by 30-50% for the same data allowance.

SIM-only versus a phone contract

A phone contract bundles a handset and an airtime plan into one monthly payment, typically over 24 or 36 months. The headline rate looks similar to a SIM-only plan, but you are paying for the phone in monthly instalments hidden in the bill. A SIM-only plan strips that out - you keep using the phone you already own, or you buy one outright when you can afford to, and you pay only for the network service. Over a typical two-year window a SIM-only owner spends £400-£800 less than someone on a comparable bundled contract. The catch is the upfront cost of the phone if yours has died.

How to switch and keep your number

Switching SIM is one of the easiest things in UK mobile. Text the word PAC to 65075 from your existing SIM and your network must reply with a free PAC code within one minute - our PAC code switching guide walks through the full process step by step. Hand that PAC to your new network when you order the SIM and your number transfers over within one working day. Ofgem rules guarantee the process is free and your old contract is terminated automatically with no early termination fee if you switched at the end of your minimum term. If you are mid-contract on a fixed plan, you may owe an early termination fee on the old account, but the PAC and number transfer themselves are always free.

Choosing the right network for you

Coverage is the single biggest variable. EE and Vodafone tend to lead 5G rollout, Three has the strongest unlimited data positioning, and O2 has historically had the best signal in rural pockets. MVNOs piggyback on the host network so the underlying signal is identical - giffgaff and 1pMobile use O2, Smarty and iD Mobile use Three, Lebara and Voxi use Vodafone. Always run your home and work postcodes through the host network is coverage checker before committing. After that, sort by price for your data tier - if you stream a lot, look at unlimited; if you mostly use Wi-Fi, even 5GB will be plenty.