Mobile Operators & SIM Cards in the United Kingdom
Checked September 29, 2026 · Sources listed at the end of the page
Three, SMARTY and Lyca Mobile all sell no-contract plans you can buy for a single month, and SMARTY also offers an eSIM. Below are dated examples from the operators' own websites, with the conditions behind the headline prices.
Prepaid offer examples
Prices from each operator's own website or announcements, checked on September 29, 2026. Offers change often, so confirm before you buy.
Pay As You Go 1 month Data Pack
- Validity:
- 1 calendar month
- Data:
- 100 GB at up to 25 Mbps (the cheaper 120 GB for GBP 13.50 headline is shown in Three's auto-renew deals, which take 10% off and add bonus data)
- Includes:
- Unlimited minutes and texts, up to 12 GB of roaming data in Three's Go Roam destinations
100GB rolling monthly plan
- Validity:
- 1 month, cancel anytime
- Data:
- 100 GB
- Includes:
- Unlimited UK calls and texts, EU roaming with a 12 GB fair-use limit, SIM or eSIM
UK Plan Mega Plus
- Validity:
- 30 days
- Data:
- 120 GB
- Includes:
- Unlimited UK calls and texts, 100 international minutes, EU and India roaming
Using your US phone in the United Kingdom
Whether your US plan covers the United Kingdom, and at what cost, depends on the plan, so check your carrier's international page before you go. Our guide to using your US phone abroad covers roaming, Wi-Fi calling and bill surprises.
To call United Kingdom from the US, dial 011 + 44 + the number: see how to call United Kingdom and the United Kingdom phone number format.
FAQ
How much does a prepaid SIM cost in the UK?
Examples checked on the operators' websites: Lyca Mobile's UK Plan Mega Plus gives 120GB for £10 for 30 days. SMARTY's 100GB plan costs £12 a month and includes unlimited UK calls and texts. Three's one-month Pay As You Go Data Pack with 100GB costs £15 and includes speeds of up to 25Mbps, up to 12GB of Go Roam data and unlimited minutes and texts.
Why is Three's advertised Data Pack price lower than the one-month price?
Three's headline Pay As You Go deal advertises 120GB for £13.50. Three says setting up auto-renew on a Data Pack saves 10% and adds bonus data on selected packs. Three's one-month Pay As You Go Data Pack with 100GB costs £15 and includes speeds of up to 25Mbps, up to 12GB of Go Roam data and unlimited minutes and texts. If you only need a pack for one trip, remember to turn auto-renew off afterwards.
Can I get a UK eSIM before I leave the US?
A SMARTY physical SIM arrives by post in 2 to 5 days, or you can start faster with an eSIM. Before using a Three SIM outside the UK, you must first make a purchase associated with the SIM in the UK so it is correctly provisioned on Three's network.
Does a UK SIM work in Europe?
Many UK plans include some EU roaming. On SMARTY you can make unlimited UK and EU calls and texts and use up to 12GB of your monthly data allowance in the EU. Lyca Mobile's 30-day bundles include up to 35GB of EU roaming data, depending on the plan.
How long does a UK pay-as-you-go number stay active?
A Three Pay As You Go number stays active only if it is used for at least one chargeable activity, such as a top-up, a Data Pack, a call, a text or internet use, every 180 days. Rules differ between operators, so check yours if you want to keep the number for your next trip.
Sources
- Three: Pay As You Go Data Packs (accessed 2026-09-29)
- SMARTY: 100GB data SIM plan (accessed 2026-09-29)
- Lyca Mobile: UK SIM Only Deals (accessed 2026-09-29)
- SMARTY: Simple, honest mobile (accessed 2026-09-29)