O2 guidance

This is the oldest lineage in British mobile. The business began as BT Cellnet, took the O2 name in 2002, and since 2021 has sat inside a joint venture alongside a cable company.

It is also the largest landlord in the market. Tesco Mobile, giffgaff and Sky Mobile all transmit on these masts, so a great many British handsets run on O2 radio under another badge. That is useful to you: it makes this the cheapest of the four networks to test properly before committing.

Coverage is broad nationally and the 5G layer keeps widening. The documented weakness has nothing to do with reach: it is how many handsets share a mast at once. In busy city centres, roughly between five and seven in the evening, the bars stay full while data crawls. Independent measurement firms have recorded the pattern for years.

The distinction matters, because congestion cannot be cured by any setting on your phone, and moving network only helps if the alternative is quieter at the same place at the same hour.

Rolling and fixed terms are both sold, unlimited is widely available, and multi-line reductions apply under one account. Choose the length by how settled your circumstances are rather than by the monthly difference.

Handset deals here are structured differently from most of the market, and better. The phone and the airtime sit on two separate agreements, so the device payment genuinely ends when the handset is paid off.

Standard credit-based service with no contract and no credit check. For regular use, the brands renting these masts generally price prepaid better than O2 does itself.

That leaves prepaid best suited here to spare handsets, a child's first phone, and testing coverage before committing to anything longer.

An eSIM is your plan written into a chip already inside the handset rather than posted on plastic. The service is identical; what changes is speed — minutes rather than days — and the ability to hold a second line alongside your main one.

That second line is what makes travelling dramatically cheaper: a local data profile for data, your UK number left live for calls and texts.

Broadband in this group means cable or full fibre — a fixed-line product decided by whether your street is wired for it, and entirely unrelated to your mobile signal. Whether your street has cable and whether your bedroom has bars are two separate questions with two separate answers.

Bundling mobile and broadband produces real household savings, particularly across several lines.

This is the genuine selling point. O2 is the only one of the four mast owners still including European roaming on standard plans rather than charging a daily fee.

It is included up to a published fair-use ceiling. Past that, per-gigabyte charging begins — which is where surprise bills actually come from, not from any visible daily charge.

At home, on the handset, unlimited is genuinely unmetered — here and on the other mast owners. Three published conditions bend it, and all three are readable before you sign.

Before buying any allowance, read three months of recorded usage in your current app. People routinely buy about twice what they consume.

Three figures get quoted at you and only one describes what you will actually pay across the agreement.

Bills rise for five reasons, every one printed somewhere before you signed.

And they fall for five, none of which happen by themselves.

Two applications run here — one for the account and one for the rewards platform — sharing a single login. That login also guards the phone number your bank sends authentication codes to, which makes the password unusually valuable to a criminal.

Most reported faults trace to one of four causes, and two are cured by free settings you already have.

One caveat specific to this network: the early-evening slowdown in busy centres is congestion rather than a fault, so support cannot fix it. Testing another network at the same place and hour is the only way to know whether moving would help.

Switching runs entirely on text messages. No conversation is required and none can be insisted upon.

Your network cannot refuse the code, sit on it, attach conditions to it, or make a retentions conversation a precondition of leaving. Retention offers are lawful and occasionally good — but take the code first, so you are choosing rather than asking.

If you are actually with Tesco Mobile, giffgaff or Sky Mobile, all of this — complaints included — goes to that brand and never to O2.

In a sentence: the best roaming terms of the big four and the clearest contract structure — spoiled a little by rush hour in the biggest cities.