Last updated: Monday 5 October 2026 (Europe/London).
Next update: when Smarty’s 40GB £7 offer or giffgaff’s 25GB and 40GB plans change price, data or terms.
By: Switch Editorial Team, Switch Squid Ltd
As of 5 October 2026, a monthly rolling SIM-only plan is cheaper than classic pay as you go for most UK users who touch mobile data every week — Smarty’s 40GB plan at £7 a month (£84 over 12 months) with unlimited UK calls and texts and no contract is our lead pick, while pure top-up pay as you go only tends to win for very light, mostly-offline phones. giffgaff’s 25GB rolling plan at £6 and 40GB 18-month plan at £8 are the closest alternatives. We may earn a commission if you buy through our links.
Sources: Smarty and giffgaff plan pages checked 5 October 2026; Uswitch — how pay as you go SIMs work; Ofcom — ban on inflation-linked mid-contract price rises; Ofcom — switching mobile provider.
Smarty 40GB — £7 a month, cancel any month
- £84 over 12 months at £7 a month while the offer price applies
- 40GB 5G and 4G data, unlimited UK calls and texts, on the Three network
- One-month plan: no annual contract, no credit check
- Main limitation: check the basket shows 40GB at £7 before you pay, and check Three coverage where you live and work
Pay as you go vs SIM-only: what the words actually mean in 2026
The labels have blurred over the years, so it helps to pin them down before comparing prices.
Classic pay as you go means you top up credit — often from about £5 at a time — and pay for each minute, text or megabyte you use. Nothing renews automatically. You stop paying the moment you stop topping up. Uswitch puts it simply: pay-per-use can work for very light users, but it is often the more expensive way to use a phone.
Pay as you go bundles are 30-day packs of calls, texts and data for a set price. You buy one, it lasts a month, and you can renew it or let it lapse. Many people who say they are “on pay as you go” are actually on one of these.
Monthly rolling SIM-only works almost the same way as a bundle but renews on a card each month until you cancel. Smarty’s one-month plans and giffgaff’s rolling plans sit here. There is no long contract and, with Smarty, no credit check.
Fixed-term SIM-only locks the price for 12, 18 or 24 months. You usually get more data for the money but cannot leave early without paying. Since 17 January 2025, Ofcom has required any mid-contract price rises in new phone contracts to be shown upfront in pounds and pence rather than linked to inflation.
So the real decision in October 2026 is rarely “pay as you go or contract”. It is “pay per use, or a fixed monthly allowance I can cancel?” For anyone who uses apps, maps or messaging most days, the allowance usually wins.
Which is cheaper for light, medium and heavy users?
Here is how the options compare across a year. The SIM-only prices are the offers checked on 5 October 2026. Pay-per-use costs depend on your network’s rates and your habits, so we describe them rather than invent a figure.
| User type | Typical habit | Best-value option | Monthly price | 12-month cost | Main catch |
|---|---|---|---|---|---|
| Very light | Phone kept for emergencies and the odd call, little or no mobile data | Classic pay as you go top-ups | Varies with use; top-ups often from about £5 | Depends on how often you top up | Pay-per-use data gets expensive fast; SIMs can be deactivated if unused for around six months |
| Light to medium | Messaging, maps and some social media, up to about 25GB | giffgaff 25GB, monthly rolling (O2 network) | £6 | £72 | Less headroom if a month runs heavy |
| Medium to heavy | Daily streaming on the commute, hotspotting now and then, up to about 40GB | Smarty 40GB, one-month plan (Three network) | £7 | £84 | Check Three coverage and that the basket shows £7 |
| Medium to heavy, happy to commit | About 40GB and sure you will keep the plan | giffgaff 40GB, 18-month plan (O2 network) | £8 | £96 (£144 over the full 18 months) | Locked in for 18 months |
| Very heavy | Regularly beyond 40GB | An unlimited SIM-only plan | Higher | Higher | See our cheapest unlimited SIM-only guide |
The pattern is clear. Once you use data most days, a fixed allowance beats paying by the megabyte, and a no-contract monthly plan gives you nearly all the flexibility people choose pay as you go for. On these figures Smarty costs £1 a month more than giffgaff’s 25GB plan but gives you 15GB more data each month, and it costs £1 a month less than giffgaff’s 40GB plan without the 18-month commitment.
Smarty 40GB — £84 over 12 months, no contract
- £7 a month for 40GB with unlimited UK calls and texts
- Cheaper over a year than the £8 18-month 40GB alternative, and you can leave any month
- Best for medium and heavy data users who want pay-as-you-go flexibility
When classic pay as you go still makes sense
Pay-per-use is not a bad choice — it is a choice for a particular kind of phone. It suits you if:
- the phone is a backup or emergency handset that stays in a drawer or glovebox most of the time;
- you are setting up a first phone for a child or an older relative and want a firm limit on spending;
- you use wifi at home and work and almost never switch on mobile data;
- you want to avoid any regular payment leaving your account.
Two things to watch. Uswitch notes that networks may deactivate a pay as you go SIM if it is not used for about six months, so make a call or send a text now and then. And unused credit or add-ons that expire are usually not refundable, so avoid topping up far more than you need.
When a monthly SIM-only plan is the better buy
Choose a monthly plan if you check maps, music or social apps on the move most days, if you have ever been caught out by credit running low mid-journey, or if you want one predictable cost each month. A month-to-month plan gives the same freedom to walk away that people value in pay as you go, but the data allowance makes daily use far cheaper.
A 12- or 18-month plan is worth it only when the monthly saving is real and you are confident your needs will not change. If you are unsure, the rolling option costs little extra and keeps your options open. Our guide to rolling vs 18-month SIM contracts goes into that choice in more detail.
How to work out which group you are in
Your phone already knows how much data you use. On an iPhone, open Settings, then Mobile Data, and look at the usage for the current period. On Android, look under Settings, then Network or Connections, then Data usage. Check the last two or three months rather than one, because holidays and busy weeks skew a single month.
- Under 1–2GB a month and mainly calls: pay as you go top-ups may cost you less.
- Roughly 5–25GB: a low-cost rolling plan such as giffgaff 25GB at £6 fits.
- Roughly 25–40GB: Smarty 40GB at £7 gives headroom without a contract.
- Above 40GB most months: look at unlimited plans — see our cheapest unlimited SIM-only guide.
How to switch from pay as you go to SIM-only and keep your number
1. Check coverage. Smarty uses Three’s network and giffgaff uses O2’s. Use each network’s postcode checker for home, work and your commute.
2. Use up or note your credit. Leftover pay as you go credit usually does not transfer to a new provider, so try to run it down first.
3. Get your switching code. Text PAC to 65075 from your current phone to get a code that moves your number. The code arrives by text and is valid for 30 days.
4. Order the new SIM or eSIM. Enter the code at checkout, or in your new account, and choose a switch date.
5. Swap the SIM on the day. Your number moves across, usually within one working day, and your old pay as you go service ends.
Fit summary
Good for: anyone on pay as you go who now uses mobile data most days and wants a lower, predictable monthly cost without a long contract.
Consider alternatives: giffgaff 25GB at £6 if you use less data and O2 coverage suits you better.
Not for: very light users who rarely use mobile data — classic top-ups may cost less.
Important conditions
- Prices and data allowances were checked on 5 October 2026 and can change. Confirm the price in your basket before you pay.
- Coverage varies by network and location.
- Pay-per-use rates differ between networks; check your own network’s rates before deciding.
- Unused pay as you go credit is usually not refundable or transferable.
- Fixed-term plans charge to leave early; rolling plans can be cancelled at the end of any month.
- We may earn a commission if you buy through our links.
Final decision card
Use data most days → a rolling SIM-only plan; Smarty 40GB at £7 is our lead pick at £84 a year with no contract.
Light data user on O2 → giffgaff 25GB rolling at £6.
Phone mostly in a drawer → stay on pay as you go top-ups and use the SIM at least every few months.
Move from top-ups to Smarty 40GB at £7
- Check Three coverage for your postcode first
- Text PAC to 65075 to keep your number
- Confirm 40GB at £7 a month in the basket before paying
FAQ
Is pay as you go cheaper than SIM-only in the UK?
Only for very light users who rarely use mobile data. Once you use apps, maps or streaming most days, a monthly SIM-only allowance is usually cheaper. As of 5 October 2026, Smarty offers 40GB for £7 a month on a plan you can cancel any month.
What is the difference between pay as you go and a rolling SIM-only plan?
Classic pay as you go charges for each call, text or megabyte from credit you top up. A rolling SIM-only plan gives a set monthly allowance for a fixed price and renews until you cancel. Both avoid long contracts.
Can I keep my number when I move from pay as you go to SIM-only?
Yes. Text PAC to 65075 to get a switching code, then give it to your new provider when you order. Your number usually moves within one working day.
Do pay as you go SIMs expire?
They can. Networks may deactivate a pay as you go SIM that has not been used for around six months, so make a call or send a text from time to time. Expired credit is usually not refundable.
Does a SIM-only plan need a credit check?
It depends on the provider. Smarty’s one-month plans do not need a credit check. Fixed-term contracts from other networks often do.
How much data do I need each month?
Check the last two or three months in your phone’s mobile data settings. Many people who mainly message and use maps need under 25GB, while daily streamers often need 40GB or more.
Can my monthly price go up during a SIM-only contract?
For new fixed-term contracts, Ofcom rules since 17 January 2025 mean any planned rise must be shown in pounds and pence before you sign. Smarty says its one-month plans have no annual price rises.
