Mobile Fundamentals · SIMs & Identity · Lesson 2 of 4

eSIM

A SIM card with no card: how eSIMs get set up.

No card required

An eSIM does the same job as a plastic SIM card, but the chip is built into the phone, usually soldered to the main board. So instead of mailing you a card, the carrier sends you a profile. The profile holds what a plastic SIM would carry, including your IMSI and the secret keys your phone uses to prove its identity to the network.

The phone downloads the profile over the internet. Common ways to start the download:

• Scanning a QR code from the carrier, in a store or by email
• Using the carrier's own app
• Transferring it from your old phone, where the carrier and phone support this
• Typing in activation details by hand

The QR code doesn't contain the profile. It holds the address of the carrier's provisioning server and a one-time activation code, and the phone uses those to fetch the profile securely.

eSIMs are handy because there's no card to lose or pull out of a stolen phone. Treat an unused eSIM QR code like a password, though. Depending on the carrier's setup, whoever scans it first may be the one who gets your line.

What's in the name

The e in eSIM stands for embedded. The GSMA, the mobile industry body that publishes the eSIM standards, uses the technical name eUICC, for embedded Universal Integrated Circuit Card. UICC is the formal name for the smart card chip inside any SIM.

Because the chip is permanent, it's built to be rewritten. One eSIM can store several profiles, so a single phone can hold a home plan, a work line and a travel plan, and you switch between them in Settings. How many profiles a phone can store, and how many can be active at once, depends on the model. Many current phones can run two lines together, using an eSIM plus a physical SIM, or two eSIMs.

Before a trip, for example, you can buy a local data plan online, install its profile, and switch to it when you land. Your home number stays on the phone the whole time.

For investigators, there's no card to seize from an eSIM phone. The profile's ICCID shows in the settings on many phones, and carrier records hold the rest. The eSIM chip also has its own 32-digit ID, the EID.