Which UK SIM-only deals are actually cheapest in 2026? Honest breakdown of Voxi, Smarty, Lebara, iD Mobile, Tesco Mobile, and GiffGaff. Best for unlimited data, low-data plans, international calls, and 5G.
The UK SIM-only market is fiercely price-competitive in 2026. Switching from a contract that bundles a handset to a clean SIM-only plan is one of the biggest single savings most UK households can make on a recurring bill — typical handset-bundled contracts cost £40–£70/month, while SIM-only equivalents on the same network often start at £8–£15/month for the same data and minutes.
This article cuts through the marketing noise across the six biggest budget SIM-only providers — Voxi, Smarty, Lebara, iD Mobile, Tesco Mobile, and GiffGaff — and shows which is actually cheapest for which use case. All six run on one of the four UK mobile networks (EE, O2, Three, Vodafone), so the underlying signal coverage is the same as the bigger network you might already be paying twice as much to use.
Quick comparison
Provider
Underlying network
Contract
Cheapest unlimited
Standout feature
Voxi
Vodafone
30-day rolling
~£20/month (3x data promo runs)
Unlimited Social Media (free WhatsApp, Insta, TikTok, etc.)
Data Rollover, EU roaming, often £30 Amazon voucher promo
Tesco Mobile
O2
1-month or 12-month
~£20/month
Clubcard points + family multi-SIM discount
GiffGaff
O2
1-month rolling, no contract
~£20/month, often less on goodybag
Easiest exit, refer-a-friend
All six are MVNOs (Mobile Virtual Network Operators) — they don't own physical infrastructure but resell capacity from EE, O2, Three, or Vodafone. Coverage and signal quality match the parent network exactly. Customer service standards differ widely.
What to actually look for in a SIM-only deal
Before the breakdowns, the four things that actually matter:
Underlying network signal at your home and work. Use your own phone's signal as a sanity check. If Three drops calls in your living room, switching to a Three-based MVNO won't fix that.
Data allowance vs realistic usage. Most light users genuinely need only 5–10GB/month. Heavy streamers genuinely need unlimited. Pay for what you actually use, not the worst-case headline number.
Contract length flexibility. 30-day rolling deals let you switch when a better promo lands. 12-month contracts lock you in but sometimes shave a couple of pounds off the monthly cost.
5G availability. All six providers above offer 5G on their parent network, but availability varies. Check the network coverage map for your postcode if 5G actually matters to you (it usually doesn't on a good 4G signal).
Best for unlimited data
Smarty is consistently among the cheapest for unlimited 5G data, with promotional pricing dropping to around £15/month for the first three months and settling around £20. Smarty also runs Data Cashback, where you get money back if you use less than your allowance — useful if your usage is unpredictable. Runs on Three's network.
Voxi matches Smarty on raw price, often £20/month for unlimited 5G (3x data promo runs frequently dropped that to even better rates in early 2026), with the bonus of Endless Social Media — apps like WhatsApp, Instagram, TikTok, Facebook Messenger, and X don't count against your data allowance regardless of plan tier. Runs on Vodafone.
iD Mobile unlimited typically lands at £16–£20/month with frequent promos and gift-card incentives. Runs on Three.
Winner: Smarty for the cleanest pure-unlimited deal, Voxi if you actually use a lot of social apps (the unmetered social can save 20GB+/month for heavy users).
Best for low-data plans (under 10GB)
Lebara dominates the cheap end. A 3GB SIM is around £4/month, 8GB around £6/month, with frequent introductory pricing dropping the first six months even lower. Runs on Vodafone.
iD Mobile matches Lebara on cheap plans and adds Data Rollover — unused data carries over to the next month, so light users with bursty usage don't waste their allowance.
GiffGaff offers "goodybags" of varying sizes; 6GB is around £8/month, 15GB around £12/month. Runs on O2.
Winner: Lebara for the absolute cheapest light-user deals, iD Mobile if you want Data Rollover.
Best for international calls
Lebara is in a class of its own here. Plans bundle minutes to dozens of international destinations (often 100+ minutes to specific countries), and the dial-out rates for unbundled minutes are among the lowest in the UK MVNO market. If you call family abroad regularly, Lebara saves real money.
Voxi has historically included reasonable international calls in its higher tiers but is not as competitive as Lebara on raw international cost.
Winner: Lebara, decisively.
Best for streaming and social media
Voxi is the clear winner. Unlimited social media (WhatsApp, Insta, TikTok, Facebook Messenger, X, Snapchat) and unlimited video on selected plans means streaming and scrolling don't dent your data. For users whose phone is mostly social, even Voxi's smaller plans can feel unlimited.
Three-based MVNOs (Smarty, iD Mobile) benefit from Three's traffic-management favouring video streaming, but the headline allowances still apply.
Winner: Voxi for social media users specifically.
Best for 5G coverage
All six providers offer 5G — but 5G availability depends entirely on the parent network's rollout, not the MVNO branding.
EE has the broadest UK 5G coverage. None of the six providers above run on EE.
Vodafone (Voxi, Lebara) and O2 (Tesco Mobile, GiffGaff) have strong urban 5G with patchy regional coverage.
Three (Smarty, iD Mobile) has aggressive 5G rollout in cities, weaker outside.
If 5G is critical to you, check the parent network's coverage map for your specific postcodes before choosing.
Winner: depends on your postcode. None of these MVNOs has special 5G — they inherit it.
Best for customer service
Which? consumer surveys consistently rank GiffGaff, Smarty, and Tesco Mobile at the top among MVNOs for customer service quality. EE-based providers (none in this list) rank highest among the major networks.
Voxi, iD Mobile, and Lebara sit lower on customer service rankings. They all work fine when nothing goes wrong, but resolution times for billing or porting issues can stretch.
Winner: GiffGaff narrowly, with Smarty close behind.
Sign-up bonuses
Several of these providers run referral schemes that pay both sides. Worth knowing about if you were going to sign up anyway:
Voxi — Currently running the Friends with Benefits programme paying £20 to £40 in gift cards (Amazon, Just Eat, or PayPal) per friend who signs up and pays for two months. Double Rewards window in spring 2026 makes this the highest-paying refer-a-friend in the SIM-only category. Active codes at /referrals/voxi.
iD Mobile — Refer-a-friend with credit (~£25) when a friend takes a contract. Active codes at /referrals/id-mobile.
Tesco Mobile — £25 voucher for the new customer on selected contracts when joining via referral.
GiffGaff — £5 each side once the new user tops up. Lower bonus, but very low friction.
Smarty — Referral typically pays a small credit on first month.
Lebara — Limited referral activity in 2026.
The Voxi Friends with Benefits programme is the standout because the reward scales by plan tier and pays out in flexible gift cards including PayPal cash. For most readers planning to switch SIM, it's worth checking that referral page first.
Provider profiles in brief
Voxi
Vodafone-owned, Vodafone-network, marketed at younger users but works fine for any age. Unlimited Social Media on every plan is the headline feature. 30-day rolling contracts with no commitment. App-based account management. Best for: heavy social media users, anyone wanting to stay flexible month-to-month.
Smarty
Three-owned, Three-network. Famously transparent pricing — no inflation-linked increases, no hidden fees, monthly rolling only. Data Cashback gives you money back on unused data. Best for: people who hate contracts and want a clean fixed-price deal.
Lebara
Vodafone-network, focused on the international-calling segment. Cheapest entry-level plans in the UK MVNO market and bundled minutes to dozens of countries. Best for: anyone calling abroad regularly, plus extreme budget users on small data plans.
iD Mobile
Three-network, owned by Currys plc. Data Rollover means unused data carries over to next month. Frequently promotional with gift-card incentives. Often the cheapest contract option for mid-tier users. Best for: people whose data needs vary month to month.
Tesco Mobile
O2-network, owned by Tesco plc. Clubcard points on monthly bills, family multi-SIM discounts, capped-cost contracts (you can set a monthly spend cap). Best for: existing Clubcard users and families wanting multiple SIMs on one account.
GiffGaff
O2-network, member-owned model. "Goodybag" monthly plans with no contract, unlimited rollover with the goodybag system. Strong community-based customer support. Best for: people who want maximum flexibility and don't mind community-style support.
Final verdict
Use case
Best pick
Cheapest unlimited data
Smarty (or Voxi during 3x data promo)
Heavy social media user
Voxi
Cheapest small-data plan
Lebara
International calls
Lebara
Data Rollover
iD Mobile
Clubcard / family SIMs
Tesco Mobile
Easiest exit, no commitment
Smarty or GiffGaff
Best customer service
GiffGaff
Highest sign-up bonus
Voxi (£20–£40 gift card)
Most UK readers should pick based on the underlying network signal in their area first, then on the feature that matches their actual usage second. All six providers above will be cheaper than staying on EE, O2, Three, or Vodafone directly for an equivalent plan.
A SIM-only deal is a mobile contract that gives you a SIM card with allowances for data, minutes, and texts but does not bundle a handset. You bring your own phone (or buy one separately, often for less than the bundled total cost). SIM-only deals are typically 30–70% cheaper than handset-bundled contracts on the same network.
Will a SIM-only deal work with my current phone?
Almost certainly yes, as long as your current phone is unlocked. Phones bought outright or after a contract has ended are usually unlocked. Phones still in the middle of a contract may be locked to the original network. You can check by inserting a SIM from a different network or contacting your current provider for an unlock.
Do MVNOs have worse signal than the big networks?
No. MVNOs run on the same physical infrastructure as their parent network. Voxi and Lebara use Vodafone's network. Smarty and iD Mobile use Three's. Tesco Mobile and GiffGaff use O2. Signal coverage and 4G/5G availability are identical to the parent network. The only difference can be data prioritisation in congested areas, where the parent network's direct customers may be served fractionally faster.
How do I switch SIM-only providers?
The Mobile Number Switching Service makes it simple. Text 65075 from your current SIM to get your PAC code, give the PAC code to your new provider during sign-up, and the switch completes within one working day with your number transferring automatically. You don't need to cancel the old contract separately — the PAC handles it.
Are 12-month contracts cheaper than monthly rolling?
Usually only marginally — typically £1–£2/month off compared to the equivalent 30-day rolling deal on the same provider. The trade-off is contract lock-in. With monthly rolling, you can switch whenever a competitor runs a better promo, which often saves more than the £1–£2/month a 12-month contract would have saved.
Which SIM-only provider is best for a teenager?
Voxi is a popular choice because Endless Social Media means heavy WhatsApp, TikTok, Insta, and Snapchat usage doesn't burn through data. Tesco Mobile's capped-cost contracts are good if you want to control how much a family member can spend in any given month.
Can I keep my old phone number when switching?
Yes. Use the PAC code system described above. Your number transfers to the new provider within one working day at no cost. Don't cancel your old contract before getting the PAC — that releases the number and makes transfer harder.
Are SIM-only deals available with 5G?
Yes. All six providers covered above offer 5G on their parent network, on plans that support it. 5G availability depends on the parent network's rollout in your specific postcode rather than on the MVNO branding.
