Why SIM-only plans are popular in the UK
SIM-only plans have become the default choice for millions of UK mobile users. Instead of locking into a 24 or 36-month handset contract, a SIM-only plan separates the cost of your phone from the cost of your service. You keep your existing handset, slot in a new SIM, and pay a much smaller monthly amount for calls, texts, and data.
The appeal is simple. Households want control over monthly bills, the freedom to switch providers when a better deal appears, and clear pricing without surprise upgrade fees. A cheap UK SIM deal can replace an expensive bundled contract for a fraction of the cost while still including unlimited minutes, unlimited texts, and 5G data on a major UK network.
Benefits of no-contract mobile plans
A no-contract SIM UK plan, sometimes called a 30-day rolling plan, gives you genuine month-to-month flexibility. There is no minimum term, no early termination fee, and no credit check in most cases. If your usage changes, you can switch to a larger or smaller plan the following month without penalty.
- Cancel or switch plans any month with no exit fees.
- Match your data allowance to how you actually use your phone.
- Avoid being tied to a handset you no longer want.
- Take advantage of new offers as soon as they launch.
- Keep total monthly mobile costs predictable.
Pay as you go SIM UK options work in a similar way for lighter users — you top up only when you need credit, with no ongoing commitment at all.
How PAC codes work
A PAC (Porting Authorisation Code) is the nine-character code that lets you move your existing mobile number from one UK network to another. It is free, and your current provider must issue it on request. To get a PAC, simply text the word PAC to 65075 from the phone you want to move. Your provider will reply within a minute with your code and any final balance information.
Once you have your PAC, you give it to your new provider when activating your new SIM. The number transfer usually completes within one working day, and you keep the same mobile number throughout — friends, family, and contacts never need to be updated.
How to keep your number when switching
Keeping your number is the most common concern when switching to a new free UK SIM card, and the process has been deliberately simplified by Ofcom. The end-to-end flow is:
- Order your free SIM from your chosen new provider.
- When the SIM arrives, activate it on the network.
- Text PAC to 65075 from your old SIM to get your transfer code.
- Submit the PAC through your new provider's number transfer page.
- Your number switches across — typically the next working day.
During the short transfer window your old SIM will stop working and the new one takes over. You do not need to cancel your old contract separately — submitting a PAC closes the old account automatically.
Why users switch to giffgaff
giffgaff is one of the most well-known no-contract mobile providers in the UK, running on the O2 network. It is popular with people who want a free giffgaff SIM, flexible monthly goodybags, and the option to switch or pause without contracts. The provider also runs a long-standing referral programme where eligible new customers can receive a £10 bonus credit after meeting the standard activation requirements.
Common reasons users choose a giffgaff SIM include:
- Free SIM card with no upfront cost.
- O2 network coverage for 4G and 5G across the UK.
- 30-day rolling plans with no credit check.
- The ability to keep an existing UK mobile number via PAC code.
- Eligibility for the giffgaff £10 bonus through a referral link, subject to current terms.
For a full breakdown of monthly costs and data allowances, see our pricing comparison, or jump to the FAQ section for quick answers about delivery, activation, and number transfers.