What is an eSIM?
It is the same thing a SIM card has always been — the chip that proves to a network which account you are — except it is built into the phone and the account is written to it over the internet.
The card, without the card
A plastic SIM is a tiny computer that stores one credential: this handset belongs to this account on this network. Everything else about it — the plastic, the tray, the paperclip — exists only so the chip can be moved between phones. An eSIM removes that. The chip is soldered into the phone during manufacture and the credential, called a profile, is written to it by download. Nothing is inserted, nothing can be lost, and one eSIM chip can hold several profiles at once.
What actually happens when you buy one
You pay, and we ask the network operator to issue a profile for you. What comes back is a QR code, which is just a compact way of writing an address and a one-time key. Your phone reads it, connects to the server at that address, proves it holds the key, and downloads the profile. That download is the entire installation. From that point the phone has a second line it can use, and the QR code is spent — it cannot be installed twice, on your phone or anyone else’s.
What it does not change
Your existing SIM stays exactly where it is, and so does your number. A phone that supports eSIM is a dual-SIM phone: it holds your normal line and the new profile at the same time, and you decide in settings which one makes calls and which one carries data. Installing a travel eSIM does not overwrite anything, does not cancel anything, and can be undone by deleting the profile.
Which phones have one
Broadly, iPhone XS and newer, Google Pixel 3 and newer, and Samsung Galaxy S20 and newer, plus a growing list from other manufacturers. The definitive test takes five seconds: dial *#06# and look for an EID number next to the IMEI. If an EID appears, the hardware is there. The second requirement trips up more people than the first — the phone must not be locked to a mobile operator, because a locked handset refuses profiles that are not its operator’s.
Why travellers care
Before eSIM, using a local network abroad meant finding a shop, showing a passport, and swapping out the SIM you rely on — which took your own number offline for the trip. An eSIM is bought from your sofa, installed before you leave, and sits alongside your own line rather than replacing it. That is the whole of the change, and it is why travel data stopped being something you sort out on arrival.
What an eSIM is not
It is not a phone number, and it is not a substitute for your contract. A travel eSIM like ours carries data only: no calls, no SMS, no number of its own. It is also not tied to one country forever — a phone can hold several profiles and you switch between them in settings, so the eSIM you used last summer stays on the handset, spent but harmless, until you delete it.