Four MVNOs use O2's network in the UK: Chattr, Giffgaff, Sky Mobile, and Tesco Mobile. All four offer the same 4G and 5G coverage as O2 itself, with different contract terms, roaming policies, and pricing. This guide explains what each one offers and how to pick the right one for your usage. Verified in May 2026.
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Reviewed by: Phil Brown, founder of SIM Only Finder. Phil previously worked in UK mobile retail at Three UK, advising customers on SIM plans, contracts, and network choices. He has spent over a decade running consumer comparison platforms and reviews networks and SIM-only deals based on that hands-on industry background. About the author
Last reviewed: May 2026. Updated regularly to reflect current plan pricing, network changes, and roaming policies.
How we put this guide together
To put this guide together, we reviewed the four MVNOs currently running on O2's network in May 2026, checking contract terms, 5G access, roaming policies, and price rise terms directly against each network's published terms. We also drew on our broader experience reviewing UK SIM-only networks and tracking how MVNO arrangements have changed over time. Coverage reliability assessments reference the most recent RootMetrics UK RootScore Report and Ofcom Connected Nations data.
What "uses O2's network" actually means
Chattr, Giffgaff, Sky Mobile, and Tesco Mobile are MVNOs (mobile virtual network operators). They do not own mast infrastructure. Instead, they buy wholesale access from Virgin Media O2 and resell SIM plans under their own brands. The signal you receive on your phone is the same O2 signal that an O2 direct customer would get in the same location.
That means 4G and 5G coverage is identical to O2 on all four. What changes between the host network and its MVNOs is the contract terms, the extras, and the price. Historically, some O2 MVNOs were slower to roll out features like Wi-Fi Calling and 4G Calling than the host network: Sky Mobile launched both early, while Giffgaff and Tesco Mobile took longer. 4G Calling, also known as VoLTE, is the technology that routes voice calls over the 4G network rather than older 2G or 3G connections, giving faster call setup and better audio quality. This matters now that UK networks have shut down 3G and are gradually phasing out 2G. Support for Wi-Fi Calling and 4G Calling varies across O2 MVNOs and across handsets, so it is worth checking your specific phone model against the network's supported devices page before switching.
One thing to note: O2's 5G picture has shifted in recent reporting. Ofcom's Connected Nations 2025 report (published November 2025) places O2 second only to EE on 5G geographic coverage, ahead of both Vodafone and Three. O2 also has the widest 5G Standalone (5G SA) footprint, covering nearly two-thirds of the UK, while EE and Vodafone are at around half. The trade-off is that O2 was the last major network to switch off 3G, so a slightly higher proportion of O2 connections still run on older 3G technology than rivals. For most users on a modern handset, the practical experience is good 5G availability with the same coverage on all four O2 MVNOs as on O2 itself.
Chattr
Chattr is one of the newer MVNOs on O2's network and offers SIM-only plans aimed at customers who want straightforward, predictable monthly costs without long contracts. All Chattr plans run on a 30-day rolling basis, so there is no minimum term and no exit fee if you change your mind.
5G is included on all plans at no extra cost, and the network supports eSIMs. EU roaming is included on all plans, and there is no credit check required to sign up. Plans come with unlimited UK minutes and texts across the range, starting from £10 per month for 5GB and rising to £20 for unlimited data, with mid-tier options at £14 for 25GB and £15 for 50GB.
Chattr's pricing is competitive at the mid-data tiers rather than rock-bottom at the low end. Customer service is handled online and through the Chattr app. The network does not currently have a physical store presence.
Best for: Customers who want O2 coverage on a 30-day rolling plan with no credit check, predictable pricing, and eSIM support. A good fit for short-term residents, students, and anyone who wants the flexibility to leave any month.
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Giffgaff
Giffgaff is the best known O2 MVNO and one of the most flexible. Almost all of its SIM-only plans run on a 30-day rolling basis, which means you can cancel or change plan any month without penalty. Giffgaff also offers 18-month plans with more data for the same money, and these come with a no mid-contract price rise guarantee.
5G is included on every plan at no extra cost, and the network supports Wi-Fi Calling, 4G Calling, eSIMs, and tethering. EU roaming is included on all plans, but plans with more than 5GB of UK data have a 5GB cap on roaming data per plan cycle, after which usage is charged at 10p per MB.
Giffgaff stands out for its self-service model. There is no call centre. Customer support is handled through community forums and online agents, which suits some people and frustrates others. Pricing is consistently among the cheapest on O2 coverage, particularly for low and mid-range data allowances. Because most plans are 30 days, the question of mid-contract price rises does not really apply, but the 18-month plans are explicitly fixed. You can read more about how mid-contract rises work across the industry in our guide to SIM-only mid-contract price rises.
Best for: Anyone who wants O2 coverage with maximum flexibility, no mid-contract price rises, and the lowest possible monthly cost. Particularly suited to people comfortable with online-only customer service.
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Sky Mobile
Sky Mobile sells 12-month SIM-only plans on O2 coverage and is best known for two features: data rollover and benefits for existing Sky TV customers. Unused data rolls over for up to 12 months and can be saved up or cashed in for rewards. Sky cut the rollover window from three years to 12 months in April 2024, which is worth knowing if you are comparing older guides. If you are a Sky TV customer, all data used to stream Sky apps does not count against your monthly allowance, which makes it a strong choice for heavy streamers already in the Sky ecosystem. Our guide to networks that offer data rollover covers how these schemes compare across the market.
5G is supported, as are Wi-Fi Calling, 4G Calling, and eSIMs. You can change your data allowance each month even mid-contract, which is unusual. The downside is roaming. Sky Mobile applies a £2 per day "Roaming Passport Plus" charge to use your plan in over 70 destinations including the EU, USA, and Australia, where Giffgaff and Tesco Mobile both include EU roaming at no extra cost. If you travel regularly, this adds up quickly.
Sky Mobile's SIM-only pricing is generally a step above Giffgaff for equivalent data allowances, reflecting the rollover and Sky-bundle extras. From 1 April 2026, Sky Mobile customers face a £1.50 per month increase. Unlike EE, Vodafone, Three, and O2, Sky's contracts do not state a specific pounds-and-pence rise at the point of sale. Their terms reserve the right to raise prices and commit to giving advance notice if they do. Affected customers have the standard Ofcom right to cancel penalty-free within 30 days of being notified of the rise.
Best for: Sky TV customers, and anyone who wants O2 coverage with the ability to bank unused data rather than lose it at the end of each month.
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Tesco Mobile
Tesco Mobile is one of the longest-established O2 MVNOs and offers a wide choice of SIM-only contract lengths, with both 12-month and 24-month terms available.
EU roaming is included at no extra cost across 48 "Home From Home" destinations with no fair usage data cap, though a broader fair usage policy applies if you spend more time abroad than in the UK. Tesco originally committed to this until 2026 and has since extended the offer into 2027. This makes it more generous than most networks including O2 itself. 5G is supported, as are Wi-Fi Calling, 4G Calling, eSIMs, and tethering. Tesco Clubcard holders can access Clubcard Prices on selected SIM-only plans, which are typically a few pounds cheaper than the standard rate and have prices frozen for the contract duration. Non-Clubcard plans are subject to annual price rises in April. Tesco's approach is unusual: rather than a flat rise across all customers, the increase is proportional to the customer's monthly price, working out at roughly 6% per year. For example, a £10 monthly plan would rise by around 60p, while a £17.50 plan would rise by around £1.05. The exact rise is shown in pounds and pence at the point of sale.
Tesco Mobile's customer service has been recognised at the Uswitch Telecoms Awards, where it won Best Mobile Network for Customer Service in 2026 for the fifth year in a row, based on Uswitch's public survey of UK mobile customers. The network also operates physical stores inside larger Tesco branches, which is useful if you prefer to handle issues in person.
Best for: Clubcard holders, people who want generous inclusive EU roaming, and anyone who values strong customer service or the option of in-person support.
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Networks that used to be on O2
Two former O2 MVNOs no longer offer O2 coverage. Lyca Mobile moved to EE's network in June 2023, so any Lyca SIM bought since then uses EE infrastructure rather than O2. Virgin Mobile ran on O2 from July 2022 until August 2023, when the brand was wound down and existing customers were migrated to O2 itself following the Virgin Media O2 merger. Virgin Mobile is no longer accepting new customers.
If you specifically want O2 coverage, the only options today are O2 itself or one of the four MVNOs above.
How to choose between O2 and an O2 MVNO
Going direct to O2 gets you access to the O2 Priority app, a 25GB inclusive EU roaming allowance, and a wider range of contract structures including custom term lengths. There is one significant catch: from April 2026, almost all O2 Pay Monthly and SIM-only customers face a £2.50 per month price rise, or £30 a year. This applies to both existing and new contracts. O2 had previously committed in customer contracts to a £1.80 annual rise, so the £2.50 figure is around 40% above the level customers signed up for. The UK government described the move as "against the spirit" of Ofcom's pricing rules, though Ofcom has not yet taken action against it.
Going with an MVNO almost always gets you a lower monthly price for equivalent data and minutes. Giffgaff is usually the cheapest and most flexible. Tesco Mobile has the best inclusive roaming and Clubcard discounts. Sky Mobile is the right answer if you already pay for Sky TV or you genuinely use rollover data. Chattr suits customers who want a 30-day plan with no credit check and predictable pricing at the mid-data tiers. Coverage is identical across all five options, including O2 itself, so the choice comes down to contract terms, extras, and price.
Conclusion
The four MVNOs running on O2's network in May 2026 are Chattr, Giffgaff, Sky Mobile, and Tesco Mobile. All four offer the same 4G and 5G coverage as O2 itself, with different contract terms, roaming policies, and pricing. Giffgaff is the cheapest and most flexible. Tesco Mobile is the best for roaming and Clubcard holders. Sky Mobile is the best for existing Sky TV customers. Chattr is the best for 30-day rolling plans without a credit check. For details on how each one's price rise terms compare across the wider market, see our guide to mid-contract price rises.
How to switch to an O2-based network
To switch from your current network to Chattr, Giffgaff, Sky Mobile, or Tesco Mobile while keeping your existing phone number, you need a PAC code from your current provider. Text PAC to 65075 from the number you want to transfer and your network will reply with the code within a minute. The code is valid for 30 days. Give it to your new network when you sign up, and your number will transfer within one working day. For network-specific switching steps, see our guides for switching to Giffgaff, switching to Sky Mobile, or switching to Tesco Mobile. For Chattr, contact the network directly through their app or online chat to start a number transfer.
If you do not need to keep your number, you can simply order a new SIM from the network of your choice and start using it straight away.
Editorial policy
This guide is produced by the SIM Only Finder editorial team to help readers compare the MVNOs running on O2's network across UK networks. Network terms, pricing, and feature availability are checked regularly and updated to reflect current offers. Always confirm current terms directly with the network before signing up.
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