What is an eSIM? A plain-English guide for travellers

What an eSIM actually is

SIM stands for subscriber identity module. It's the small piece of technology that tells a mobile network who you are, which plan you're on and which network you're allowed to use. For thirty years it came as a plastic card that you pushed into a tray on the side of your phone.

An eSIM (embedded SIM) does exactly the same job, but the chip is soldered inside the phone at the factory. Instead of receiving a plastic card, you download the plan onto that chip. Think of it like the difference between buying a film on DVD and downloading it: the film is the same, only the delivery changes.

The chip can store several plans at once. You might have your home plan, a work plan and a travel plan for Japan all saved on the same phone, and switch between them in Settings.

The technology is standardised by the GSMA, the body that sets the rules for mobile networks worldwide. That's why an eSIM bought from one company works in phones from Apple, Google, Samsung and many others.

How an eSIM works

When you buy an eSIM plan, the provider creates a digital profile for you: a small, encrypted file containing the same details a plastic SIM would carry. Your phone downloads that profile over the internet and stores it on its eSIM chip.

There are three common ways to install it:

1. One-tap install link. On iPhones running iOS 17.4 or later, you can tap a link on the install page or in your email, and the phone takes you straight to the install screen.
2. QR code. You scan a QR code with the phone's camera, or in the eSIM settings, and the phone downloads the profile. You need a second screen (another phone, a laptop or a printout) to show the code.
3. Manual codes. If scanning doesn't work, you type in two codes: an SM-DP+ address and an activation code. It takes a minute longer but does the same thing.

Once the profile is installed, it sits on your phone as an extra line, usually labelled something like "Travel" or "Business" until you rename it. When you arrive and switch that line on, the phone connects to a partner network in that country, exactly as it would with a local SIM card.

eSIM vs a physical SIM card

The big win for travellers is that you can set everything up from your sofa before you leave. No queue at an airport kiosk after a long flight, no language barrier, no hunting for a paperclip to open the SIM tray.

Why travellers use eSIMs

When you land abroad, you have roughly four ways to get online. Here's how they compare in practice.

Travel eSIMs sit in a sweet spot: close to local SIM prices, without the shop visit, and your home SIM stays in your phone so you still receive bank codes and calls.

Will my phone work with an eSIM?

Most phones made since 2018 support eSIM. As a rough guide:

• iPhone: iPhone XS, XS Max, XR and every model since, including the iPhone SE (2nd generation and later). iPhone 14 and later models sold in the US have no SIM tray at all, so they are eSIM-only.
• Google Pixel: Pixel 3 and later.
• Samsung Galaxy: S20 and later, every Z Fold and Z Flip, and a growing number of A-series models.
• Others: many recent phones from Motorola, OnePlus, Oppo, Xiaomi, Sony and others, but support varies by model and by the country the phone was sold in.

Two things matter as much as the model:

1. Your phone must be carrier-unlocked. If your phone came on a contract and is locked to your carrier, it can't use another network's eSIM until it's unlocked. Most carriers unlock phones on request once the contract terms are met.
2. Where the phone was sold. Some phones sold in mainland China don't include eSIM, even when the same model elsewhere does.

The quickest check: on an iPhone, go to Settings → General → About and look for a section called Digital SIM or Available SIM. On Android, look in Settings → Network & internet → SIMs for an option to add an eSIM or download a SIM. Or use our phone check, which covers hundreds of models.

How to set up a travel eSIM, step by step

Before you fly

1. Check your phone supports eSIM and is unlocked (see above).
2. Buy a plan for your destination. Pick one that covers your trip length with some data to spare.
3. Install it on Wi-Fi. Use the one-tap link on iPhone, or scan the QR code. It takes two or three minutes.
4. Rename the line to something you'll recognise, like "kimsim Japan". On iPhone: Settings → Mobile Service → tap the line → Mobile Plan Label.
5. Leave it switched off until you travel, if you like. With kimsim the plan doesn't start until it first connects at your destination, so installing early costs you nothing.

When you land

1. Turn on the eSIM line in your settings.
2. Choose it for mobile data. On iPhone: Settings → Mobile Service → Mobile Data → pick your travel line.
3. Turn on Data Roaming for the eSIM line. This is the step people miss most often. Your phone sees a travel eSIM as roaming, so the switch must be on, but only for the travel line.
4. Keep your home line on for calls and texts if you want to receive them, but turn off data roaming on your home line so you aren't charged by your carrier.

Within a minute or so you should see signal bars and a network name. That's it: you're online.

Keeping your number, WhatsApp and bank codes

A common worry is "Will I lose my number?" No. A travel eSIM is an extra line. Your normal SIM, physical or eSIM, stays in your phone.

• WhatsApp, iMessage, FaceTime, Telegram and Signal are linked to your account, not to the line carrying the data. They keep working on your usual number over the travel eSIM's data.
• Normal calls and SMS to your number still reach your home SIM if you leave that line switched on. Your home carrier may charge roaming rates to answer calls, so check before you pick up.
• Bank and app verification texts keep arriving on your home SIM. That's a big advantage over a local SIM card, which replaces your home SIM.

How much data do you need?

It depends far more on what you do than on how long you stay. These are rough figures and vary by app, settings and network:

For a typical week of maps, messaging, some social media and the odd video call, many travellers use somewhere around 3–7 GB. If you stream video or use your phone as a hotspot for a laptop, plan for much more, or choose an unlimited plan.

What "unlimited" really means

Many travel eSIMs advertise "unlimited" data. In practice that almost always means a daily allowance at full speed, after which your speed is reduced until the next day starts.

At kimsim we only call a plan Unlimited when the reduced speed is 1 Mbps, which is enough for messages, maps, email and music, though not HD video. Plans that slow down further are called Day Pass, and every plan shows its after-cap speed before you pay. If a provider doesn't tell you the speed after the cap, ask.

Data only: what that means

Most travel eSIMs, ours included, are data only. You get mobile internet, but no local phone number for calling or texting. For most travellers that's fine: messaging and calls happen through apps.

If you need a local number, for example to receive calls from local businesses, some countries offer tourist SIMs with a number, usually as a physical card that needs ID.

Common problems and quick fixes

"No service" after landing. Check that the eSIM line is switched on, selected for mobile data, and that Data Roaming is on for that line. Then turn Airplane Mode on and off once. This fixes most cases.

Signal bars but no internet. Check the APN settings. Most eSIMs set them automatically, but if your eSIM comes with an APN, enter it under the line's mobile data network settings. Restarting the phone also helps.

The QR code won't scan. Increase the screen brightness, try again from a slightly greater distance, or enter the codes manually.

"This code is no longer valid." The eSIM may already be installed. Look for an extra line in your settings before trying again, because most eSIMs can only be installed once.

My phone calls it "Business" or "Travel". That's just the label your phone gave the new line. Rename it in your SIM settings.

How many eSIMs can one phone hold?

More than you'll ever need for travel. Apple says an iPhone can hold eight or more eSIMs, and with Dual SIM it can use two lines at once. Recent Android phones also store several eSIM profiles, though the exact number depends on the model.

What matters is that two lines can be active together: your home line for calls and texts, and the travel eSIM for data. Every other eSIM you've installed simply sits switched off in your settings, ready for the next trip. Some recent iPhones sold in the US have no SIM tray at all and only take eSIMs, which is one reason travel eSIMs have become the normal way to get data abroad.

What happens to the eSIM after your trip?

Nothing, unless you want it to. When the plan's days run out, or the data is used up, the line just stops connecting. It doesn't charge you, and it doesn't renew on its own.

You have three choices:

• Keep it for next time. If you go back to the same country, or your plan covers a region you'll visit again, you may be able to top up the same eSIM instead of installing a new one.
• Switch it off. Turn the line off in your settings so the phone doesn't keep trying to use it. Your home line goes back to being the only line.
• Delete it. If you're sure you won't use it again, you can remove it. Read what to do with an eSIM after your trip first: a deleted eSIM usually can't be reinstalled, so delete only when the plan is finished for good.

eSIM or pocket Wi-Fi?

A pocket Wi-Fi is a small rented router that you carry around and connect your phone to. It used to be the standard answer for countries like Japan and South Korea, and it still suits some groups: one device can share its connection with several phones and laptops.

For most travellers, an eSIM is simpler:

• Nothing to collect or return. A rented router usually has to be picked up at the airport or delivered to your hotel, and sent back before you fly home.
• Nothing to charge. The router has its own battery. When it runs flat, everyone sharing it loses the internet.
• Nobody gets left behind. With a router, the person carrying it is the only one online when the group splits up. With an eSIM, each phone has its own connection.
• It works the moment you land. You install the eSIM at home, so there's no queue at a rental counter after a long flight.

If several people need data, each can have their own eSIM, or one phone can share its connection as a hotspot for a while.

Is an eSIM safe?

Yes, and in some ways safer than a plastic SIM. The profile is encrypted and downloaded over a secure connection, and it can't be pulled out of a lost or stolen phone and used in another device. It's protected by your phone's passcode and security, and you can delete it from your settings at any time.

As with any purchase, buy from a provider that shows clear prices, after-cap speeds and a refund policy before you pay.

Is a travel eSIM worth it?

For most trips abroad, a travel eSIM is the simplest and cheapest way to stay online: buy it at home, install it on Wi-Fi, and switch it on when you land. The only real requirements are a phone from roughly the last six or seven years, and that it isn't locked to your carrier.

If you're not sure your phone supports eSIM, check it here. Then pick your destination: Japan, Thailand, the United States, or see all destinations.