Best SIM only deals: how to pick the right network.
SIM only is the cheapest way to run a phone you already own – no handset cost, just data, calls and texts, often on a plan you can leave with 30 days’ notice. The catch is choice: a dozen UK networks all claim the best deal. The honest answer is that the best SIM only deal depends on what you value – so here is which network genuinely wins for each priority, updated monthly. Compare live prices on our SIM only comparison.
Best for unlimited data.
SMARTY and Three consistently price unlimited data lowest – SMARTY on flexible 30-day rolling terms over Three’s 5G network, Three itself cheaper still if you’ll commit to 12 or 24 months, with hotspot use included. Vodafone and O2 cost more for unlimited but add entertainment perks and O2 Priority extras.
Best under £10 a month.
Light users are spoilt: ASDA Mobile, iD Mobile and Talkmobile all run solid allowances below £10, on Vodafone’s and Three’s networks. iD Mobile stands out for data rollover – unused data carries into next month – which effectively stretches a small allowance.
Best 30-day rolling (no commitment).
SMARTY, VOXI, giffgaff and Lebara are built around rolling plans: leave or change allowance every month. Perfect between contracts, for students, or while you decide whether a cheap plan covers your real usage.
Best with no credit check.
Because rolling plans carry no long-term commitment, giffgaff, SMARTY, Lebara and VOXI don’t run hard credit checks – ideal if you’re new to the UK, rebuilding credit, or just prefer not to add a search to your file. Pair one with a refurbished SIM free phone and you have a flagship-quality setup with no credit agreement anywhere.
Best for perks and extras.
VOXI gives unlimited social media data (TikTok, Instagram and more don’t touch your allowance). O2 brings Priority tickets and offers. Sky Mobile rolls unused data into a pot for up to three years and discounts for Sky TV households. Lebara includes international minutes to 41 countries – unbeatable for calling abroad.
Best coverage.
Every network here runs on one of the four UK infrastructures: EE (Spusu), O2 (giffgaff, Sky Mobile), Vodafone (VOXI, Lebara, Talkmobile, ASDA Mobile) or Three (SMARTY, iD Mobile). Pick by which signal is strongest where you live – the budget brands get the same masts as their parent networks.
How to switch in two minutes.
Text PAC to 65075, get your code, give it to the new network – your number moves across, usually the next working day. Your old contract ends automatically. That’s it.
SIM only + refurbished: the smart money setup.
The cheapest way to run a great phone in 2026: buy it refurbished and SIM free (graded, tested, 12-month warranty), put a cheap SIM in it, and trade in your old handset to cover a chunk of the cost. No 24-month handset contract, no interest, and you can switch network whenever a better deal appears.
Ready to compare live prices? See all SIM only deals across every network above.