Last updated: 5 September 2026
By Stiv · Design, technology and personal finance
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The best SIM only deals UK in 2026 are not coming from EE, Vodafone, O2, or Three. They come from the challengers running on the exact same infrastructure at a fraction of the monthly cost. Three stand out right now: Honest Mobile, Smarty, and giffgaff. Each one has a distinct edge, and together they cover pretty much every type of mobile user. Every price below was re-checked at source on 5 September 2026, the week giffgaff cut unlimited data on an 18 month contract to £14 a month and Smarty quietly narrowed its unused-data refund.
Why going SIM only in 2026 makes sense
Most phone contracts bundle in the cost of a handset alongside your data, calls, and texts. Once that phone is paid off, you are often still paying the same monthly amount. Going SIM only removes that dead weight entirely. You keep your number, you usually get more data for less money, and you can switch every 30 days if you find a better deal.
If your existing phone is in good shape, or you picked up a refurb from somewhere like Back Market, a rolling SIM only plan is almost always the smarter financial choice. Ofcom data shows that many UK consumers are paying above-market rates through legacy contracts with mid-year price rises baked in. A monthly rolling SIM from a challenger network fixes both problems.
The best SIM only deals UK 2026: our three picks
Honest Mobile: best for long-term value and ethical credentials
Honest Mobile runs on Three's network and puts 5G on every plan. Its loyalty discount takes the bill down every month you stay, up to 30% off, which is the opposite of the direction most mobile bills travel. Unlimited costs £25 and falls to £17.50 once the discount has built. Honest Mobile does not publish the monthly rate at which it builds, so treat £17.50 as the floor rather than a date you can plan around.
Current rolling 30-day plans:
| Data | Monthly price | With max loyalty discount |
|---|---|---|
| 4 GB | £12.15 | £9.45 |
| 10 GB | £17.50 | £12.25 |
| Unlimited | £25.00 | £17.50 |
All plans include 5G, Wi-Fi calling and unrestricted hotspot. The unlimited plan is capped in one way the name hides. Honest Mobile's own plan page marks it "Limited to 3G speeds after 750GB". Roaming is 5 days free per trip, with up to 20 GB a month on unlimited, 10 GB on the 10 GB plan and 4 GB on the 4 GB plan. Honest Mobile is carbon negative and a certified B Corp, which puts it in a different category from most MVNOs. eSIM is available at sign-up. There is also a referral offer for new sign-ups, see our Honest Mobile referral code page for details.
Prices are correct at time of writing. Always verify directly with the provider before signing up.
See our Honest Mobile guideSmarty: best for pure value on Three's network
Smarty is one of the cheapest networks in the UK by any measure. It runs on Three's infrastructure, all plans are 30-day rolling, there is no credit check, and there are no annual price rises. Plans start at £6 a month for 5 GB and climb through 40 GB at £10 and 100 GB at £12, with unlimited at £20. That unlimited price alone sets it apart from most of the competition.
The unused-data refund Smarty used to be known for has narrowed a long way. Its help centre now describes the data discount as applying to "all SMARTY small data plans, (1GB, 2GB and 3GB)", says it is discontinued for new customers, and rules it out on rolling monthly plans. Group plans are the saving that is still open. Two to eight people share one account, the first member on Everyone Unlimited pays £20 and every extra member pays £15, and a mix-and-match group saves 10% on the plans brought into it.
Smarty now sells eSIM to new customers directly, and its own eSIM page opens with "Join SMARTY instantly with an eSIM, no waiting around". The setup is covered in full on our Smarty service guide. A referral bonus is also available, see our Smarty refer a friend page for the current offer.
See our Smarty guidegiffgaff: best for O2 coverage, flexibility, and community perks
giffgaff runs on O2's network, and O2 took Best Mobile Network Coverage at the Uswitch Mobiles Awards 2026, judged on Opensignal data. Prices are split across three tabs and the same money buys different things on each. Monthly rolling starts at £6 for 2 GB; pay as you go starts at £6 for 1 GB. The 18 month contracts are where the value sits at the moment: 80 GB for £10, 100 GB for £15, and unlimited data at £14 a month against a standard £25. giffgaff dates that unlimited price to 11.59pm on 2 October 2026. No contract plan carries mid-contract price rises.
Naturally, there is a lot more to giffgaff than one headline price. Our full guide to giffgaff plans walks through every goodybag tier, the 18 month contracts and the joiner credit in detail, while this roundup stays on the comparison across networks.
The community-based customer support model is divisive. It works well if you are comfortable with forums, less so if you prefer a phone line. What is less divisive is the coverage and the track record. giffgaff scored 94% overall satisfaction in Ofcom's most recent Comparing customer service report, against an 88% industry average. It won Mobile Network of the Year at the Uswitch awards in 2025, and Best Mobile Handset Contract Network in 2026. eSIM is available at sign-up. Payback pays members £5 for every mate they bring on board, but it arrives as points and cashes out twice a year, in June and December.
If Three's network does not perform well in your area, giffgaff and its O2 backbone is the obvious alternative among the three picks here.
See our giffgaff guideWhat about eSIM? A quick explainer
All three networks in this comparison support eSIM. An eSIM is a digital SIM built into your device. You activate it with a QR code sent by email, rather than waiting for a plastic card in the post. Most phones released in the last few years support it, including iPhone XS and later, and a wide range of Android devices from Samsung, Google, and others.
The main practical advantage is speed of activation. If you want to switch networks the same day or run two numbers on one phone (useful for separating work and personal, or keeping a home network SIM alongside a travel one), eSIM makes it seamless.
All three now offer eSIM at the point of sign-up. giffgaff and Honest Mobile have done so for a while, and Smarty's eSIM page now promises new customers they can "Join SMARTY instantly with an eSIM, no waiting around".
How to switch: it takes about 10 minutes
Switching SIM only providers is significantly simpler than most people expect. To keep your existing number, text PAC to 65075 from your current SIM. You will receive your PAC code by text within about 60 seconds. Enter that code when you sign up with your new provider, and the number transfer happens automatically, usually within 30 minutes and sometimes up to 24 hours.
You do not need to cancel your old contract first. The PAC process handles the close of your old account automatically once the number moves. Your old SIM stops working when the transfer completes, so do not activate the new one until you are ready.
Which of the best SIM only deals UK is right for you?
If budget is the only criterion and you are comfortable with Three's coverage, Smarty wins outright. If you want O2 coverage, a community support network, and flexible or contract-based options with stable pricing, giffgaff is the pick. If you want a monthly bill that falls over time, strong ethical credentials, and the best long-term deal for unlimited data, Honest Mobile is the one to choose.
All three are considerably cheaper than the big four networks. None require a credit check. All include 5G. The main variable is which network's coverage works best where you actually use your phone, so check each provider's coverage map before committing.
Frequently Asked Questions
What is the cheapest SIM only deal in the UK right now?
Both start at £6 a month, and Smarty gives you far more for it: 5 GB against giffgaff's 2 GB on monthly rolling. giffgaff runs on O2, which may perform better where you live. Prices change regularly, so check both directly before signing up.
What network does Smarty use?
Smarty runs on Three's network, which is in the process of merging with Vodafone to form VodafoneThree. Coverage reaches around 99% of the UK population on 4G, with 5G available in most cities and towns at no extra cost on any Smarty plan.
Does giffgaff include 5G?
Yes. All giffgaff plans now include 5G at no extra charge, via O2's network. You will need a 5G-compatible device and to be in an area with 5G coverage. There is no premium tier required to unlock it.
Is Honest Mobile worth the higher entry price?
Honest Mobile's entry-level plans cost more than Smarty or giffgaff on day one. However, the loyalty discount means long-term customers pay progressively less each month. For the unlimited plan in particular, Honest Mobile becomes highly competitive once that discount builds, and no other MVNO in this comparison reduces its price over time in the same way.
Can I keep my phone number when switching SIM only networks?
Yes. Text PAC to 65075 from your current SIM. You will receive your porting code by text within around 60 seconds. Give this to your new provider when you sign up or activate your new SIM. The transfer completes automatically, usually within 30 minutes to 24 hours. You do not need to cancel your existing plan manually.
Which network offers the best eSIM support?
giffgaff and Honest Mobile both offer eSIM directly at sign-up. Smarty sells eSIM to new customers too, so none of the three needs a plastic card first. All three require a compatible device, which includes iPhone XS onwards and most recent Android flagships.
Are these SIM only deals suitable for 5G phones?
Yes. All three networks, Honest Mobile, Smarty and giffgaff, include 5G access on all plans at no extra cost. Coverage varies by location, so it is worth using each provider's coverage checker with your postcode to confirm 5G availability in your area before switching.
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