What is an eSIM? A plain explanation for travellers

An eSIM is a SIM that's built into your phone instead of being a plastic card you insert. You download a small profile from a carrier, the phone stores it on a dedicated chip, and from then on it behaves like any other line: it connects to a mobile network and carries data, and on normal phone plans, calls and texts too. A travel eSIM, like the ones Cabin Mode sells, is a data-only line for another country that you install before you fly and switch on when you land.

That's the whole idea. The rest of this page covers how it works, what it changes when you travel, and where the limits are.

The short definition

eSIM stands for embedded SIM. The chip, called an eUICC, is soldered onto the phone's board at the factory. It can hold several carrier profiles at once, and you add or remove them in software rather than with a SIM tool and a paperclip.

A physical SIM card does two jobs: it proves to the network who you are, and it stores the settings needed to connect. An eSIM does exactly the same two jobs. The only difference is how the identity gets onto the phone: downloaded over the internet rather than posted in an envelope or handed over a shop counter.

How an eSIM gets onto your iPhone

Every eSIM starts as a profile sitting on a carrier's provisioning server (the technical name is SM-DP+). Getting it onto your phone takes one of three routes:

One-tap install from an app. The carrier's app hands the profile details straight to iOS. You tap Install, confirm a couple of screens, and it's done. This is how Cabin Mode installs by default.
QR code. You scan a code with the camera (or from Settings › Cellular › Add eSIM) and iOS downloads the profile it points to.
Manual entry. You type in the SM-DP+ address and an activation code. Slower, but it works when the other two don't.

All three need an internet connection, usually Wi-Fi, because the phone has to reach the provisioning server. That's why the standard advice is to install a travel eSIM at home before your flight. The full walkthrough is in how to install a travel eSIM on iPhone.

One rule surprises people: a profile can generally only be downloaded once. If you delete it, you can't scan the same QR code again and get it back. Think of it as a SIM card you've cut in half. More on that in can you reuse or delete a travel eSIM.

eSIM vs physical SIM card

	Physical SIM card	eSIM
How you get it	Posted, or bought in a shop	Downloaded over Wi-Fi
Swapping lines	Eject the tray, swap the card	Change a setting
Lines stored	One per slot	Eight or more on current iPhones
Lines active at once	One per slot	Two (on iPhone 13 and later, both can be eSIMs)
Can be lost or damaged	Yes	No
Moving to a new phone	Move the card	Transfer or re-issue, depending on the carrier
Works on a carrier-locked phone	Only your carrier's	Only your carrier's

The last row matters. An eSIM doesn't get around a carrier lock. If your iPhone is locked to your home carrier, it won't accept another provider's eSIM any more than it would accept their physical SIM card. Check Settings › General › About › Carrier Lock and look for "No SIM restrictions".

Which phones have an eSIM

On iPhone, every model from the iPhone XS, XS Max and XR (2018) onwards supports eSIM, as do the iPhone SE (2nd generation) and later. From the iPhone 14 onwards, US models have no SIM tray at all, and the iPhone 17 and iPhone 18 Pro lines are eSIM-only in a dozen countries including Canada, Mexico and Japan. The full list, with the dual SIM details, is in which iPhones support eSIM.

Many recent Android phones also support eSIM. Cabin Mode is iPhone-only, so this guide sticks to iOS.

What a travel eSIM is

A travel eSIM is a prepaid data plan for somewhere you're visiting: one country, or a region such as Europe. It differs from your normal line in three ways:

It's data only. No phone number, no calls, no SMS. You keep your usual SIM or eSIM for those, side by side.
It's prepaid and fixed. You pay once for an amount of data (say 10 GB) and a validity period (say 30 days). No contract, no bill afterwards.
It connects as a roamer. The line connects to local partner networks in the destination, which is why you turn Data Roaming on for it. You're not paying roaming rates; that's just how the phone labels a line that isn't on its home network.

In practice, you end up with two lines on one iPhone: your home line for calls, texts and bank codes, and the travel line for mobile data. You tell iOS which line carries data in Settings › Cellular › Cellular Data (called Mobile Data in some regions). Dual SIM on iPhone explains how the two lines share the work.

Why travellers use one

Before eSIMs, being online abroad meant one of three things: paying your home carrier's roaming rates, buying a local SIM card at the airport, or renting a pocket Wi-Fi router. Each still has its place, and we compare them honestly in eSIM vs roaming vs a local SIM and pocket Wi-Fi vs eSIM.

What an eSIM changes:

You're online when you land. The line is already on the phone. You switch it on as the plane taxis in, and maps and messages work before you reach passport control.
Nothing to swap. Your home SIM stays where it is, so you keep receiving calls and texts on your usual number, including bank verification codes. See keeping WhatsApp and bank codes abroad.
It usually costs less than roaming. As an example, a 10 GB, 30-day Japan plan in Cabin Mode is $9.40 (prices checked 25 September 2026, shown in your own currency in the app). A US carrier's international day pass is typically $12 a day. More on that in how to avoid roaming charges on iPhone.
It fits multi-country trips. A regional plan covers several countries on one eSIM. Whether that beats separate country plans depends on the route; see regional vs country eSIM.

What an eSIM can't do

Worth knowing before you rely on one:

It doesn't give you a local phone number. Some ride-hailing, restaurant booking and delivery apps want a local number. If you need one, a local SIM is the better fit.
It needs an unlocked phone. No way around this; ask your carrier to unlock it before you go.
It depends on the local network. A travel eSIM rides the same towers as local customers. If there's no coverage in a mountain valley, there's no coverage for you either.
It won't work at sea or in the air on ships' and planes' own networks. See using an eSIM on a cruise or plane.
It has an expiry. Validity counts down once the plan starts, whether you use the data or not.

How a Cabin Mode eSIM works, start to finish

Pick a destination and a size in the app. Browse destinations to see plans and prices, such as Japan, Europe or the United States.
Pay with Apple Pay or a card. Payment is handled by Stripe.
Install the eSIM on Wi-Fi at home with one tap. A QR code and manual details are there as a fallback.
When you land, set the travel line as your cellular data line and turn Data Roaming on for it.
Most plans start on the first network connection at your destination; a few start when installed. The plan screen tells you which.
If you run low, top up. The extra data goes onto the same eSIM, so there's nothing new to install.

Not sure how much data to buy? How much data do you need for a trip has the arithmetic, and our eSIM glossary covers the jargon you'll see along the way: ICCID, EID, APN and the rest.

Frequently asked questions

What is an eSIM in simple terms?

A SIM card you download instead of insert. It's a chip built into the phone that stores a carrier's profile, so you can add a mobile line by scanning a code or tapping a button, with nothing physical to swap.

Is an eSIM better than a physical SIM card for travel?

For most trips, yes. You can install it before you fly, you're online when you land, and your home SIM stays in the phone for calls and texts. A physical local SIM card still wins if you need a local phone number.

Does an eSIM give me a phone number?

A normal carrier eSIM does. A travel eSIM usually doesn't: it's data only. Your usual number stays on your home line, and iMessage, FaceTime and WhatsApp keep working over the travel eSIM's data.

Do I need Wi-Fi to install an eSIM?

You need an internet connection, because the phone downloads the profile from the carrier's server. Home Wi-Fi before your flight is the easiest option. Cellular data on your home line also works, but that may be roaming if you're already abroad.

Can I have two eSIMs on one iPhone?

Yes. Current iPhones store eight or more eSIMs, and iPhone 13 and later can have two active at the same time: your home line and a travel eSIM.

Does my phone need to be unlocked to use an eSIM?

Yes. A carrier-locked iPhone only accepts that carrier's eSIMs. Check Settings › General › About › Carrier Lock. "No SIM restrictions" means it's unlocked.