Before you start

An unlocked handset, or one that supports eSIM
A Cardiff address, for a contract or broadband
A UK bank account, for a contract Direct Debit

Step-by-step

1
Buy a pay-as-you-go SIM or activate an eSIM on arrival
Sold in supermarkets, phone shops and online with no identity registration at all. A UK number in your first hour unlocks bank verification, NHS appointment systems and delivery notifications, all of which assume you have one.
In personWho: YouDay 1
2
Do not attempt a 24-month contract in your first weeks
Contracts run a credit check and require a UK bank account and address. With no UK credit file you will be declined or asked for a deposit. Rolling one-month SIM-only plans have no credit check and are excellent value.
OnlineWho: You
3
Take a SIM-only plan and buy the handset separately
A rolling SIM-only plan with a large data allowance costs a fraction of a bundled handset contract over the same period and can be switched monthly. Buying the phone outright is almost always cheaper in total.
OnlineWho: You
4
Keep your number when you switch
Text PAC to 65075 and you receive a porting authorisation code by return, valid for 30 days. Ofcom rules require the switch to complete in one working day. Never cancel the old service first — that is how people lose the number.
Mobile appWho: You
5
Order broadband the day you have an address
UK installation takes one to three weeks and may need an engineer visit. Cardiff has extensive full-fibre coverage from Openreach and from alternative networks, but it is street by street rather than citywide across the older terraced stock — check the exact postcode against more than one provider, because both price and achievable speed differ.
OnlineWho: You
6
Check coverage on your actual commute, not just in the city
Urban coverage across Cardiff is strong on all four networks. The Valleys lines north — Pontypridd, Merthyr, Aberdare, Treherbert — run through steep, narrow valleys where mobile coverage is genuinely patchy and the operators differ from one another. If you will spend an hour a day on that train, compare coverage maps for the line specifically.
OnlineWho: You

Documents you’ll need

Nothing at all for pay-as-you-go
A Cardiff address and bank details, for a contract
Passport, occasionally requested for a contract

Things most newcomers don’t know

The UK has no SIM registration, unlike most of Europe.

Germany, Spain and France all require identity verification to activate a SIM. The UK requires nothing for pay-as-you-go, so a working UK number is a fifteen-minute errand rather than a first-week project.

Source: Ofcom

Text PAC to 65075 — switching keeps your number in one working day.

Ofcom requires networks to issue a porting authorisation code by text on request and complete the switch within one working day. Most people never learn the shortcode and stay on an expired contract tariff for years, which is exactly what the networks are counting on.

Source: Ofcom — switching mobile provider

Coverage falls off a cliff a few miles up the Valleys, and the maps flatter it.

The topography north of Cardiff is steep-sided narrow valleys, which is the hardest terrain in the country for mobile signal. Someone commuting in from Pontypridd or Merthyr will lose signal on stretches of the line regardless of which network they pick, and the networks are not weak in the same places. Ask people who do the journey which one they use.

Source: Ofcom — mobile coverage checker

Rolling SIM-only plans dramatically beat handset contracts, especially with no credit file.

A two-year bundle costs far more in total than a handset bought outright plus a rolling plan, locks you in, and requires the credit check a new arrival will fail. The SIM-only route sidesteps the decline and the lock-in at once.

Source: community-reported

Common mistakes to avoid

Signing a 24-month handset contract in your first weeks and being declined or asked for a deposit.
Cancelling the old service before requesting a PAC code, and losing the number.
Taking the first broadband offer without checking which networks reach that exact address.
Assuming a Cardiff coverage map describes a commute up the Rhondda or Taff valleys.
Not knowing that pay-as-you-go requires no identity check at all.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.