Last updated: 5 November 2026
The simplest way to choose between a rolling SIM and an 18-month plan is to compare the monthly price, the minimum term and any price rises against how long you will keep the SIM. On 4 November 2026, iD Mobile 25GB was £6 a month on a 30-day rolling plan in the iD Mobile basket opened from this page. For a lot of data, Mozillion 80GB was £9.90 a month on a 1-month plan or £9 a month on a 24-month plan, as listed on Mozillion’s site on 4 November 2026. giffgaff’s 18-month plans are the other common long term: its £10 a month plan gives 25GB, as listed on giffgaff.com on 4 November 2026, and our giffgaff £10 plan guide covers it. For unlimited data, Smarty Unlimited was £17 a month rolling when you open Smarty from this page (£20 on Smarty’s own site), as listed on 4 November 2026, and O2’s own site listed O2 Classic Unlimited at £23 a month on a 24-month plan as a limited-time price on 1 November 2026.
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iD Mobile 25GB — £6 a month, 30-day rolling
- 25GB of data with unlimited UK calls and texts, £6 a month in the iD Mobile basket opened from this page, as listed on 4 November 2026
- £0 upfront, then £6 a month, and you can leave any month
- Runs on Three’s network. Confirm 25GB and the monthly price in the iD Mobile basket before you pay
Offer facts (prices as listed between 27 October and 4 November 2026)
Plan | Term | Price | Data | Catch |
|---|---|---|---|---|
iD Mobile 25GB (iD Mobile basket from this page, 4 November 2026) | 30-day rolling | £6/mo | 25GB | Three network; leave with a month’s notice |
Mozillion 80GB (as listed on 4 November 2026) | 24 months | £9/mo | 80GB | Two-year term; Mozillion says no mid-contract price rise |
Mozillion 80GB (as listed on 4 November 2026) | 1-month rolling | £9.90/mo | 80GB | No long contract |
Smarty Unlimited (deal price, as listed on 4 November 2026) | 1-month rolling | £17/mo | Unlimited | Three network; £20 on Smarty’s own site |
O2 Classic Unlimited (O2’s own site, as listed on 1 November 2026) | 24 months | £23/mo | Unlimited | Rises £2.50 each April; O2 listed £23 as a limited-time price on 1 November 2026, so check O2’s page for the price on the day you order |
Smarty 32GB (Smarty’s own site, as listed on 1 November 2026) | 1-month rolling | £8/mo | 32GB | Three network |
Mozillion 30GB | 1-month rolling | £7.90/mo | 30GB | No long contract |
Lebara 30GB | 30 days | £10 every 30 days | 30GB | Vodafone network |
giffgaff runs on O2 and Smarty runs on Three. Coverage differs by postcode, so check each network at home and work before you commit.
Mozillion 80GB — £9 a month on a 24-month plan
- 80GB with unlimited UK calls and texts and EU roaming in 41 countries, as listed on Mozillion’s site on 4 November 2026
- £9 a month on a 24-month plan; Mozillion says there is no credit check and no mid-contract price rise
- Main limitation: a two-year commitment. Check coverage at your postcode and confirm 80GB and £9 on Mozillion’s page before you pay
Rolling vs longer contracts: what to compare
Compare three things in the basket before you choose: the monthly price, the minimum term and any April price rises. Mozillion listed 80GB at £9 a month on a 24-month plan and £9.90 on a 1-month plan on 4 November 2026, and says its prices do not rise mid-contract. O2 lists a £2.50 rise each April on its Airtime Plans, so a 24-month O2 plan costs more in its second and third billing years than in its first. A rolling plan lets you leave at a month’s notice, which is worth paying a little more for if your plans may change.
When rolling wins
You might move, change job or travel within the next few months.
You want to test coverage before committing.
You expect your data use to change.
You want to avoid early termination charges.
Rolling plans can cost more a month than a long contract for the same data. At around 25GB, though, iD Mobile’s 25GB rolling plan at £6 a month in the basket opened from this page, as listed on 4 November 2026, cost less each month than any of the contracts above.
When a longer contract wins
Coverage at home and work is proven.
You use a lot of data and the contract costs less for the same allowance: on 1 November 2026, Mozillion 80GB was £9 a month on 24 months against £9.90 a month on its 1-month plan.
You can live with an early termination charge if your plans change.
You have read the April rises in the contract summary.
Mid-data rolling options
If you use around 16GB to 30GB, a smaller plan costs less than unlimited. On 1 November 2026, Smarty’s own site listed 32GB at £8 a month and 5GB at £6. On 27 October 2026, Mozillion’s 30GB 1-month plan was £7.90 and Lebara’s 30GB 30-day plan was £10. See our best SIM only deals guide for more.
Switching steps
Check coverage on O2 (giffgaff, O2) and Three (iD, Smarty) for home, work and your commute.
Check your monthly data use in your phone’s settings.
Text PAC to 65075 if you are keeping your number.
Decide rolling or contract before you reach the payment page.
Confirm the price in the basket, then order and port your number.
Put any contract end date in your diary.
For brand-against-brand unlimited detail, see giffgaff vs Smarty unlimited.
Smarty Unlimited — £17 a month, 1-month rolling
- Unlimited data with unlimited UK calls and texts on Three’s network, as listed on Smarty’s site on 4 November 2026
- £17 a month when you open Smarty from this page (£20 on Smarty’s own site), and you can leave any month
- Main limitation: Smarty lists a 12GB fair use limit for EU roaming. Check Three’s coverage at your postcode and confirm £17 on Smarty’s page before you pay
FAQ
Is a rolling or an 18-month SIM better?
It depends how long you will keep it and how much data you need. On 4 November 2026, iD Mobile 25GB was £6 a month on a 30-day rolling plan in the iD Mobile basket opened from this page, and Mozillion 80GB was £9 a month on 24 months or £9.90 on a 1-month plan. Compare the monthly price and the minimum term against how long you expect to stay.
How much data does giffgaff’s £10 plan give?
giffgaff’s £10 a month plan gives 25GB a month on an 18-month plan, as listed on giffgaff.com on 4 November 2026. Check giffgaff’s plan page for the allowance on the day you order.
How much is unlimited data on a rolling plan?
On 1 November 2026, Smarty Unlimited was £17 a month on a 1-month rolling plan when you open Smarty from this page, or £20 on Smarty’s own site. You can leave or change plan at the end of any month.
How much is O2 Classic Unlimited a month?
On 1 November 2026, O2’s own site listed it at £23 a month on a 24-month plan as a limited-time price, rising to £25.50 from April 2027 and £28 from April 2028. Limited-time prices can change, so check O2’s page for the price on the day you order.
Can I leave a 24-month SIM early?
Yes, but expect an early termination charge. Read the contract summary before you order.
Which network is giffgaff on?
giffgaff uses O2’s network. iD Mobile and Smarty use Three.
Can I keep my number?
Yes. Text PAC to 65075 and use the code once your new SIM is ready.
