SIM-only vs pay monthly: which really saves you money
If your phone bill hasn’t changed in years, that’s not loyalty being rewarded — it’s usually money being wasted. The single biggest mobile mistake in the UK is staying on a “pay monthly” contract after you’ve finished paying for the handset. Let’s untangle the two ways to buy a phone, and work out which one actually leaves you better off.
This is information, not financial advice. It explains how mobile tariffs work so you can make your own choice. We don’t take commission from any provider mentioned.
The two ways to pay
Pay monthly (a bundled contract) rolls two things into one price: the handset (spread over, usually, 24 or 36 months) and the airtime (your calls, texts and data). It feels convenient — a shiny new phone for one monthly fee — and it effectively spreads the cost of an expensive phone at 0% interest.
SIM-only is just the airtime. No handset, so it’s far cheaper per month — often £6–£15 for a generous plan — and usually on a rolling 30-day or 12-month deal. You bring your own phone.
Neither is automatically “better”. The right answer depends on one question: do you already own your phone, or do you need a new one?
The trap that catches millions
Here’s the problem with bundled contracts. Say you take a 24-month deal at £40 a month. After two years, the phone is fully paid for — but on most traditional contracts, the price doesn’t drop. You carry on paying £40 for a phone you now own outright, when the airtime alone might be worth £10.
That gap is pure waste, and huge numbers of people sit in it for years simply because nothing prompts them to look. The fix is free: check your end date, and if you’re past it, either move to SIM-only or ask about a cheaper deal.
Split contracts are the exception worth knowing about. Some providers now separate the device and airtime into two agreements (O2’s Custom Plan is the best-known). When the device part is paid off, that charge stops and your bill genuinely falls. If you like buying phones on a plan, a split contract avoids the overpayment trap.
So which is cheaper?
Over a two-to-three-year period, buying a handset outright and pairing it with SIM-only is often the cheapest route overall — you avoid any margin baked into the bundled price, and you’re free to switch airtime whenever a better deal appears.
But “cheapest overall” assumes you can pay for the phone up front. If finding £600–£1,000 for a flagship handset in one go isn’t realistic, a bundled or split contract spreads it interest-free, which has real value. The trade-off is flexibility: you’re locked in for the term.
A middle path many people miss: you don’t need the newest phone. A one- or two-year-old model, bought outright or refurbished, plus a cheap SIM, is where the biggest savings usually live.
About those mid-contract price rises
Mobile contracts used to sneak in yearly increases tied to inflation — typically “CPI plus 3.9%” — which almost nobody understood when they signed up. Ofcom banned that. Since 17 January 2025, any in-contract price rise must be set out in pounds and pence, upfront, at the point of sale, so you know the exact amount and timing before you commit.
Prices can still go up — but you’ll see the figure in advance rather than being surprised by a percentage. And if a provider ever raises prices in a way that wasn’t made clear when you signed, you can usually leave penalty-free. It’s another reason to read what the increase actually is before signing a long contract.
How to switch — in one working day
Switching mobile provider is far easier than most people expect, thanks to Ofcom’s text-to-switch system. From your phone:
- Keeping your number? Text PAC to 65075. You’ll get a code (a PAC) back within a minute. Give it to your new provider and they’ll move you — number and all — within one working day.
- Not keeping your number? Text STAC to 75075 instead.
- Just want your end date and any early-exit charge? Text INFO to 85075.
These texts are free, and your old provider isn’t allowed to give you the runaround or transfer you to a “retentions” team to talk you out of it.
Your next move
If you’re out of contract and own your phone, you’re the person with the most to gain — likely tens of pounds a month. Check what you actually use, then compare SIM-only deals ranked on the price you’ll genuinely pay.
Last checked 23 July 2026. Switching short-codes and the Ofcom pricing rules are current as of this date.
Sources
Just so you know: this guide is information and journalism, not financial advice, and we don't recommend specific financial products. Your circumstances are your own — if you need personal advice, speak to a suitably qualified adviser. Information was correct at the "last updated" date above but things change; always check the linked primary sources.