What is an eSIM?

An eSIM is a SIM card directly integrated into your device by the manufacturer. 

It does not need to be inserted into your smartphone and can be programmed remotely. 

The operation of the eSIM is identical to a physical SIM card. 

Only the installation of the eSIM profile and the activation is slightly different.

The next generation of SIM tech - eSIM

An eSIM, or "embedded SIM" is the next generation of SIM technology. Unlike the traditional SIM card that has to be inserted into a device, an eSIM comes, as the name suggests, pre-embedded into your device as a tiny chip (module). This module can be written onto with the necessary information and be used just like a traditional SIM. Since the eSIM module is prebuilt into the device it cannot be removed or switched between devices.

For a mental picture, an eSIM chip in terms of size is about half the size of a traditional nano SIM card.

The biggest difference in base technology between eSIMs and their physical SIM counterparts is that the subscriber information (Profile) is not written onto the SIM card by default. Instead, the profile can be downloaded from the internet and be saved onto and/or rewritten onto the eSIM module.

Until now the change of subscriber information that was previously done when inserting the SIM card into your device, can be performed with an eSIM capable device simply by downloading a profile from different network providers via internet.

A great comparison for this transition to eSIMs is the change from CD/DVD rentals to downloading of content through the internet. It used to be that you had to rent a CD/DVD from a store or have it sent to your home through a subscription service. However now, all this can be done by downloading the content through the internet, able to be enjoyed wherever you are. There is no need to insert and remove a physical disk into a CD/DVD player. Furthermore, because playback is now able to be done on smartphones, tablets, and computers, the "player" hardware (disk slot) is no longer a necessary feature.

Another great comparison to this shift in tech are gaming consoles. Until only a couple years ago (up to about the Nintendo DS), software was purchased and used on physical game cartridges, however, now on the latest consoles like the Nintendo 3DS or Switch, the software can be downloaded digitally straight to your device over the internet.

In almost exactly the same fashion, until now the SIM card, which just like the name suggests, was a physical card (like the game cartridge) is now able to be downloaded over the internet directly onto your device. This downloading of the software on to your device allows you to change network/providers freely just like you would game software.

Here is an example of what the difference looks like in the image below.

Until now the Profile containing the subscriber information (carrier information, user contract information, etc.) was came already pre-loaded onto the SIM card. eSIM's on the other hand, come as a chip pre-built into your device (technical name: eUICC or Embedded Universal Integrated Circuit Card). This chip can have your profile data written onto it after downloading the profile from the internet.

"eSIM" and what it's referring to can change based on context

The above image shows what used to be the all in one chip (hardware) and the preloaded profile (software) is now with eSIMs, separated into two parts. The actual chip or module (eUICC) that comes pre-built into the device is sometimes referred to as an eSIM but the profile you download onto the device is also sometimes referred to as an eSIM as well.

The former, again as the name suggests, is the physical pre-built SIM module which in technical terms what eSIMs actual definition best represents. However, in practice and especially in conversations/online blogs or forums both the module and the profile are commonly referred to as eSIMs. (for example, "I used multiple eSIMs" gets thrown around a lot)

The point here is that depending on the context what eSIM is referring to can change however, if you just take the time to understand the bigger picture of the actual function of the eSIM (which is what this article aims to do) you should be able to converse on the topic with no trouble.