eSIMs abroad, and the detail that decides which one to buy

EE will sell you a Roam Further pass for Mexico at five pounds ninety one a day. Ten days of that is fifty nine pounds, for the privilege of using data you have already paid for at home. O2 will do the same thing for seven pounds a day. Go without a pass at all and the per-megabyte rates in some destinations run to several pounds, which is how people come home to a phone bill longer than the hotel bill.

An eSIM for the same trip costs about a tenner. That is the entire argument, and everything below is detail.

What it actually is

An eSIM is a SIM card as software. Your phone already has the hardware; you are buying a profile that gets installed onto it, which then connects you to a local network in the country you are standing in. There is nothing to post, nothing to collect at the airport, and nothing to lose in a hotel room.

The part people find hardest to believe is that your normal SIM stays where it is. Your UK number keeps working for calls and texts, and the eSIM handles data alongside it. You switch between them in settings, and after the first time it takes about four seconds.

Mexico, which is where this became obvious

We have used Airalo across a number of trips and Mexico is the one that settled the argument. It connected before we had left the airport building, ran at proper 4G through Mexico City and down the coast, and never once dropped to the crawl you get from a cheap local SIM sold at a kiosk.

In most destinations you should see somewhere between twenty five and sixty megabits down, which is enough for a video call from a rooftop rather than merely enough for maps.

The tethering question, which decides it

If you work while you travel, this is the specification that matters and it is the one buried three pages deep on every comparison site: can you hotspot it to a laptop.

Plenty of travel eSIMs either block tethering outright or throttle it hard enough to make a video call unusable, and they tend not to say so until after you have paid. It is worth twenty seconds on the plan's own terms page before you buy, because the marketing page will never mention it. We ran a full working day off a hotspot in Mexico, calls included, and it held.

Hotel wifi is the thing you hope will work. A hotspot is the thing that does.

One caveat, and it applies across the field: on the unlimited plans, full speed usually runs to around three gigabytes a day, after which you drop to about one megabit until midnight local time. One megabit is fine for messages and maps and useless for a call. If you are working properly, buy a fixed data allowance rather than an unlimited plan, because the unlimited ones are the ones with the daily ceiling.

Who else is out there

Airalo, Nomad, Saily and Holafly are the four names you will keep meeting, and they are more alike than their marketing suggests: none of them owns a network, all of them are reselling access to local carriers, and the differences come down to which carrier they have struck a deal with in a given country, how they price data, and their tethering rules.

So compare on three things and ignore the rest. What the plan costs per gigabyte rather than per plan. Whether it permits hotspotting. And which local network it actually rides on in the country you are going to, which the better providers will tell you before you buy and the worse ones will not.

The regional plans are usually the better buy if you are crossing borders. A Europe plan covering forty-odd countries on one profile beats buying six of them.

Where it is less good

It is not a phone line. You get data and nothing else, so no local number, and anything that insists on sending an SMS to a Mexican number will not work. Your UK number still receives texts as normal, which covers most banking codes, but it is worth knowing before you rely on it.

Coverage follows whichever local network the plan is riding on, so a city will be quick and a mountain valley may not. That is true of any SIM, including the one you already have.

And your phone has to support eSIM. Every iPhone from the XS onward does, as do recent Pixels and Samsungs. Anything Android and older than about 2020 is worth checking before you buy, because installation on those can mean scanning a QR code off another screen.

How to actually do it

Buy it before you fly, on the wifi at home, where a problem is a mild irritation rather than a crisis in an arrivals hall.

1. Install the app and buy the plan for your destination.
2. Install the eSIM profile when it prompts you. Two minutes.
3. Leave it switched off until you land.
4. On arrival, turn on the travel line and turn data roaming off on your UK one. That second half is the bit people forget, and it is the bit that produces the bill.

Is it worth it

For a ten day trip outside Europe, you are choosing between roughly sixty pounds of roaming passes and roughly ten pounds of eSIM. Inside Europe the gap narrows, and if you are on a UK tariff with free EU roaming it may not be worth the bother at all for a short trip.

Everywhere else it is the cheapest useful thing you can do to a holiday, and not really because of the money. It is that landing somewhere with working data changes the first two hours of a trip, and the first two hours set the tone for the rest of it.