eSIMs, Roaming and Staying Connected Abroad

An eSIM is a SIM card built into the phone that can be provisioned by download instead of by post. Practically, it means you can buy a local data plan for the country you are visiting, install it before you leave home, and switch to it on landing — without removing your existing SIM or changing your phone number.

When an eSIM is clearly right

• Long trips outside your home region. If your plan charges daily roaming, a two-week trip at a daily rate frequently costs more than a month's local data plan.
• Multi-country trips, where regional eSIMs covering a continent are usually far cheaper than roaming in each country in turn.
• Anywhere your carrier treats as expensive. Carriers price roaming by zone and the zone boundaries are arbitrary. Check yours before assuming.

When it is not worth it

If you are travelling inside a region your plan already covers at no extra cost — much of Europe for European customers, for instance — an eSIM adds cost and complexity for nothing. And for a short trip, a few days of a modest daily roaming charge can be less than the hassle of managing a second line.

The things people get wrong

1. A data eSIM does not give you your phone number. Most travel eSIMs are data-only. Calls and texts to your normal number still arrive over your original SIM, which means roaming charges unless you disable it. Keep the home line active for texts, use the eSIM for data, and turn home data roaming off.
2. Two-factor codes by SMS. If your bank texts codes to your home number, you need that line reachable. This is the most common way a well-planned eSIM setup fails at the worst moment — at a hotel desk, trying to pay.
3. Install before you fly. Downloading an eSIM profile requires internet. Doing it on arrival, at an airport with no connection, is a solvable problem you should not have created.
4. Check your phone is unlocked and eSIM-capable. Most phones from the last few years are. Some carrier-supplied handsets are not.
5. Coverage is a network, not a country. An eSIM rides on a specific local network. In rural areas one network may work where another does not.

At sea, everything changes

This is the part that produces genuinely alarming bills. Once a ship is out of range of land, phones connect to the ship's own satellite cell service, which is not roaming in any normal sense and is not covered by any eSIM, regional plan or roaming bundle. It is billed at maritime rates, which can be several pounds or dollars per megabyte.

A phone left on with background updates enabled can generate a substantial bill overnight while you sleep. The failure is invisible: you did nothing, the phone did.

• Turn off data roaming entirely before you sail, and leave it off. Use the ship's wifi package instead.
• Airplane mode plus wifi is the safe configuration on a ship.
• In port, the ship's satellite service may still be the strongest signal in the terminal building. Walk into town before turning data on, or select the local network manually.
• Buy the ship's package if you need to be reachable. It is expensive and it is cheaper than the alternative.

What to actually do

1. Check what your existing plan charges for the specific countries you are visiting.
2. If that is expensive, buy a regional eSIM and install it at home.
3. Turn off data roaming on the home line; keep the line active for SMS codes.
4. Test the eSIM before you leave.
5. If any part of the trip is on a ship, turn data roaming off entirely and use wifi only.

The short version

• eSIMs win on long trips, multi-country trips and expensive zones. They lose on short trips inside your existing coverage.
• Data-only eSIM means your number still needs the home line for SMS — including bank codes.
• Install and test before you fly.
• At sea, no eSIM or roaming plan applies. The ship's satellite service bills at maritime rates.
• Airplane mode plus wifi is the correct setting on a ship, from sailaway to disembarkation.