Best SIM Only Deals UK 2026: Honest Mobile, Smarty and giffgaff

Last updated: March 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. Here is what sets them apart.

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 offers 5G on every plan. Its standout feature is a loyalty discount that reduces your bill by 0.41% every month you stay, stacking up to a maximum 30% off over time. The unlimited plan starts at £25/month and can fall as low as £17.50/month if you stick around long enough. In a market where bills typically climb, that direction of travel is unusual and genuinely worth noting.

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. Honest Mobile is also carbon negative and a certified B Corp, which puts it in a different category entirely 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 guide

Smarty: 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 from around £6/month, with the unlimited plan sitting at £20/month at the time of writing. That unlimited price alone sets it apart from most of the competition.

One detail worth noting: on capped plans, Smarty gives you money back for any data you do not use at the end of the month. It is a simple perk, but most networks do not bother with it. Smarty also offers a group plan option where households or couples can save 10% per additional SIM added to the account.

Smarty launched eSIM support in 2025 and it now appears as an option on their plans page. New customers may currently need to activate a physical SIM first and then request an eSIM swap via the dashboard — the process is quick and 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 guide

giffgaff: best for O2 coverage, flexibility, and community perks

giffgaff runs on O2's network, which covers around 99% of the UK population. Plans — known as goodybags — start from £6/month for 2 GB, with a monthly rolling unlimited plan at £35/month. If you are happy to commit to 18 months, the value improves significantly: 75 GB for £10 or 300 GB for £15, with no mid-contract price rises on either.

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 took Uswitch's Mobile Network of the Year award in 2025 and scored 94% overall satisfaction in Ofcom's most recent service quality report. eSIM is available at sign-up. There is also a Payback scheme where you earn £5 credit for each friend you refer.

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 guide

What 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 via 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.

Of the three, giffgaff and Honest Mobile offer eSIM directly at the point of sign-up. Smarty added eSIM support in 2025 and is rolling out full new-customer eSIM ordering — new customers can currently sign up, receive a physical SIM, and request a swap to eSIM via their account dashboard straight away.

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, 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 — and that is worth checking via each provider's coverage map before committing.

Frequently Asked Questions

What is the cheapest SIM only deal in the UK right now?

Smarty and giffgaff both offer plans from around £6/month on rolling 30-day contracts, both with unlimited calls and texts. Smarty typically offers more data at entry level, while giffgaff runs on O2 which may perform better in your area. 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 added eSIM support in 2025 and is rolling out full eSIM ordering for new customers — in the meantime, new customers get a physical SIM and can switch to eSIM via the dashboard immediately after activation. 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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