Technology

eSIM explained: how phone carriers changed

By Leandro Bruzaferro · · 6 min read
AI-generated illustration of a smartphone motherboard with an embedded eSIM chip highlighted in blue light, representing how mobile carriers changed with eSIM technology
SharePostLinkedInFacebook

The small plastic card that identified you to a mobile network survived for three decades with only changes of size. It is now disappearing, and the replacement is not a smaller card but the absence of one. The chip is soldered to the board and the identity is delivered as software, which sounds like a minor engineering detail and turns out to change the relationship between customers and carriers.

What replaced the plastic SIM

An eSIM is an embedded secure element built into the phone, capable of holding one or more carrier profiles. The profile is the part that used to live on the removable card: the subscriber identity, the authentication keys, the network configuration.

Because the chip is permanent and the profile is data, provisioning becomes a download rather than a delivery. The GSMA standardised this as Remote SIM Provisioning, which is why a profile issued by a carrier in one country works on a phone bought in another without anyone shipping anything.

The security model is deliberately similar to what it replaced. The authentication keys stay inside the secure element and are not readable by the operating system or by apps. What changed is the logistics, not the trust boundary.

How activation works

In practice you will meet one of three flows.

A QR code is the most common: the carrier issues a code that encodes the address of a provisioning server and an activation token, your phone reads it, fetches the profile and installs it. Nothing sensitive is in the code itself, which is why carriers can email it safely, but it is single-use, which is why re-scanning a saved screenshot usually fails.

Carrier apps handle the process in-app, which is smoother and locks you to a workflow the carrier controls.

Direct transfer moves a profile between two of your own devices, and it is the flow that has improved most, because the alternative was calling support to have a profile reissued.

Each flow fails in its own way, which is worth knowing before you are standing in an airport:

Flow How it works Where it breaks
QR code Encodes a provisioning server address and a single-use activation token The token is spent on first use, so a saved screenshot will not work a second time
Carrier app Provisioning handled entirely inside the operator’s own application Depends on that operator’s systems, which are least reliable at smaller carriers
Direct device transfer Profile moved between two devices you own Requires both devices working, so it is useless when one will not power on

The third row is the one that matters most, because it is the flow you will want precisely when it is unavailable.

The important operational detail: a profile is tied to one device at a time. Moving to a new phone means transferring or reissuing it, not copying it, and a profile deleted without a transfer generally has to be reissued by the carrier.

Switching carriers and dual profiles

Two consequences follow from provisioning being software, and they point in opposite directions.

The first favours the customer. Signing up no longer requires a shop visit or a wait for post, so switching is a ten-minute decision. Removing that friction is genuinely significant, because friction was doing quiet work in retaining customers who intended to leave.

The second favours nobody in particular but changes behaviour: most eSIM phones hold several profiles and keep two active at once. A work number and a personal number on one device stops requiring two devices. A local data plan can sit alongside a home plan that keeps your number reachable.

That capability is why the travel market moved first, and why a category of data-only providers exists that would have been impractical when every customer needed a card posted to them.

Travel and roaming implications

For travel, the practical gain is straightforward. You buy a local data profile before departure, install it on arrival, and keep your usual number active for calls and messages without paying roaming rates for data.

There are details worth knowing before relying on it.

Data-only travel profiles usually do not carry a usable voice line, so calls continue over your home number or over the internet. Regulations in some countries require identity registration for a local number, which a remotely provisioned profile does not always satisfy. And emergency calling behaviour with multiple profiles varies by device and network, which is worth checking rather than discovering.

The larger caution is unglamorous: install the profile while you still have working connectivity. Downloading a profile requires a network, and arriving in a country with no data and an uninstalled travel plan is the most common way this goes wrong.

Where eSIM causes friction

The technology is a clear improvement in most respects and worse in a few, and the worse cases follow a pattern: they are all situations where physically moving an identity between devices was the solution.

Borrowing a phone becomes hard. Dropping your card into a friend’s handset for an afternoon has no direct equivalent.

A broken phone is a bigger problem. With a card, you move it to a spare and continue. With an eSIM, the identity is stranded in a device that may not power on, and recovery goes through the carrier.

Second-hand value and resale get complicated by profiles that must be removed cleanly before transfer.

Support quality varies enormously. The flows depend on the carrier’s provisioning systems, and smaller operators frequently have the least reliable ones.

Coverage gaps persist in prepaid and regional markets, where the card remains the default and eSIM support is partial or absent.

There is also a structural point worth noticing. When your network identity is provisioned remotely, the ability to activate, transfer or suspend it sits with the carrier’s servers rather than in your hand. In ordinary use that is invisible. It is a different distribution of control from the one the plastic card implied, and the people who care about it are not wrong to.

For most users the summary is simple. eSIM makes changing carriers and travelling cheaper and faster, at the cost of making device failure and device borrowing harder. If you travel, the trade is clearly worth it. Either way, learn the transfer flow for your phone before you need it, not while standing at an airport.

Sources