What is an eSIM and how does it work?
An eSIM is a SIM you download. There's no plastic and no tray to open: you scan a QR code and the phone adds a new line next to the one you already have. Inside, it does exactly what the usual card does — identify you to a mobile network — except the chip comes soldered into the phone and what gets installed is the profile.
Updated on
The difference, in one sentence
A normal SIM is a chip with your details inside that goes into the phone. An eSIM is a chip that's already inside the phone and gets the details put into it. That's all. The rest of the explanation is the consequences of that switch.
The consequence that matters when you travel: you can have two lines at once. Your Spanish number for calls and WhatsApp, and a data line for the country you're going to, without taking anything out or losing anything.
What happens when you buy one
- You get a QR code by email, instantly.
- You scan it from your phone's settings, on Wi-Fi. That downloads the profile.
- The profile stays saved and switched off until you activate it.
- When you arrive at your destination, you switch on the line and the phone connects to a local operator.
- Your plan's days start counting at that moment, not before.
Downloading the profile needs a connection; activating it doesn't. That's why the instruction is always the same: install it at home on your Wi-Fi and leave it ready. If you wait until you land, you need internet to get internet.
What a travel eSIM is not
- It isn't a card with a phone number: travel plans are data only, with no number and no SMS.
- It doesn't replace your line: your usual SIM stays in and keeps receiving calls.
- It isn't a subscription: you pay once and it expires on its own, with no renewals you didn't ask for.
- It isn't a device: there's nothing to pick up, charge or return.
Which phones support it
If it's an iPhone XS or later, a Pixel 3 or later, a Galaxy S20 or later, or almost any flagship from recent years, yes. It has to be free of operator lock. To settle any doubt there's a two-second trick: dial *#06# and, if an “EID” shows up among the codes, your phone supports eSIM.
What it's really for when you travel
For not arriving in a country without data. Outside the European Union your tariff doesn't travel with you, and the usual alternatives — your operator's roaming, a local SIM bought there, a rental device — cost money, time or both. The eSIM takes the errand out of the destination and puts it on your sofa.
Does the eSIM replace my SIM card?
No. It's added as a second line. Your usual SIM stays inside the phone and keeps receiving calls and SMS on your number; the eSIM handles only the data.
Can I install it on two phones?
No. The profile downloads once and is tied to that phone. If you're switching phones before the trip, install it on the new one.
Does WhatsApp work with a data eSIM?
Yes, and it stays linked to your usual number. Everything that runs on data works the same: WhatsApp, Maps, Uber, email or your bank.
Does it use more battery than a normal SIM?
Not noticeably for being an eSIM. What does drain battery is having two active lines searching for network at once; if you're not going to use the Spanish one for data, leave it for calls only.
What happens when the data runs out?
The eSIM stops providing service. You can buy another and install it on the spot, with no waiting.
Something off, or a price changed? Write to ayuda@zasesim.com and we'll fix it. Data when you land.