An eSIM is a SIM card built into your phone. You buy a plan online, scan a QR code, and your phone carries two lines at once — your home number and local data.
Two ten-second checks before you buy anything.
Settings → General → About. Scroll to the bottom. If you see "Available SIM" or an EID number, you have eSIM. iPhone XS and newer, excluding the iPhone SE (2nd gen) in some markets.
Settings → About phone → Status, and look for an EID. Or dial *#06# — if an EID appears alongside the IMEI, you're set. Covers most Pixel, Samsung Galaxy S/Note/Fold and recent mid-range devices.
Do this at home on wifi, a day or two before you fly. Not at the airport.
Choose your country or region, data allowance and duration. You'll get a QR code by email and in the provider's app, usually within a minute.
iPhone: Settings → Cellular → Add eSIM. Android: Settings → Network → SIMs → Add eSIM. Point the camera at the code on another screen or print it out.
Name them something obvious like "Home" and "Travel". This is what stops you accidentally roaming on the wrong line later.
Mobile data: the travel eSIM. Calls and SMS: your home line. Then turn data roaming off on the home line and on for the travel eSIM — this step is the one people skip and it's the one that produces a bill.
Most plans start counting from first connection to a network, not from purchase. Land, turn the line on, and you're connected in a minute or two.
They're data-only. Almost every travel eSIM gives you data and nothing else — no local phone number, no traditional calls or SMS. WhatsApp, FaceTime and Signal all work fine over data. Bank verification codes sent by SMS arrive on your home line, which is why you keep it active.
They don't replace coverage. An eSIM roams onto local networks. If there's no signal in an Icelandic valley, no provider fixes that.
They usually can't be moved. An installed eSIM profile is generally tied to that device. Deleting it typically means it's gone for good, so don't remove one mid-trip.