How the eSIM works – and what it’s good for

Sooner or later, the SIM cards to be inserted into the device will be shut down. Over the decades they have shrunk from credit card size to mini and micro format and today, as nano SIMs, are no bigger than the little fingernail. Soon they could be gone completely.

This is made possible by the eSIM, which has been around for seven years. It replaces the physical SIM card with one that is firmly soldered into the device. The eSIM contains the same data as a conventional SIM card. These can be downloaded via an Internet connection, saved on the module and then used just like in a conventional SIM card.

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By 2025, around a third of the smartphones in use around the world should connect via eSIM, predicts the GSMA, the global industry association of mobile network operators. Actually, that would be a fine thing for customers and providers. Providers save themselves the time-consuming mailing process, and customers can use a new SIM card directly when ordering online. But somehow the change to the new technology may not really get going.

Only upper-class smartphones have an eSIM built-in – at Google, for example, the Pixel 3, and at Apple, all current models. At Samsung you can only find the eSIM in the top devices, currently for example in the Galaxy Note20 and the current Galaxy S21 5G. At Huawei it is the P40 and P40 pro models. The latest flagships from OnePlus, on the other hand, do not have an eSIM on board. Oppo and Xiaomi do not offer any models with eSIM.

eSIMs can also be found in some tablets, especially in current iPad models and high-quality business notebooks. The manufacturers are happy to install them in wearables such as the Apple Watch or the Samsung Galaxy Gear S2. In principle, the eSIM could be used in any device that is equipped with cellular access.

The eSIM has a major advantage for device manufacturers: You no longer have to plan a SIM drawer. If all the openings to the outside for the charging sockets, headphone connection and also the SIM drawer are omitted, a smartphone can be constructed much easier and cheaper, completely dustproof and waterproof. Motorola has already taken this step with the Razr 2019 and has omitted the conventional SIM. However, the device was only sold in small numbers in Germany.

When it comes to wearables, size is another important factor: the eSIM is a tiny chip that can be packaged in a suitable place on a circuit board. A SIM drawer, on the other hand, requires a comparatively large volume and can only be placed on very specific surfaces or edges of the housing, making the device more voluminous and mechanically more sensitive and restricting the freedom of the designer.

Such drawers are also prone to mechanical defects. Customers who insert cards incorrectly or force manually inaccurately cut cards into the device can seriously damage it. And even if the customer does everything right: despite the gold coating, sliding contacts always remain a possible source of error.

There is also potential in the card for cell phone providers and consumers. With an eSIM, new customers can access the network within minutes of signing an online contract. If a device is lost, the replacement device can be used immediately after uploading the eSIM data without having to order a physical replacement card. The expensive logistics for SIM cards from production to shipping are no longer necessary. Instead, SIM card profiles can be created as required and transferred to the eSIM in the customer’s device within a few seconds.

What is a convenience gain with normal mobile phone contracts and devices is a must for IoT devices. In systems that are built into the depths of industrial plants, household appliances or motor vehicles, you can’t just change the SIM card. The eSIM allows this not only contactless, but ultimately even fully automatically if required in cooperation with the provider. The use of eSIMs is already widespread in IoT applications and the market is growing rapidly because more and more devices use an Internet connection.

For smartphones, an eSIM is usually found in dual SIM devices. It can replace the second SIM card, for example on the Samsung Galaxy S21, where you can use a physical SIM on the second slot or the eSIM as SIM2. The iPhones only have one SIM slot, where the eSIM exclusively takes on the role of the second SIM.

The memory content of the physical SIM card contains the IMSI (International Mobile Subscriber Identity), i.e. the serial number of the SIM card, and information about the home network. With the eSIM, this data is stored in a profile. The eSIM can save several of these, and the user can switch back and forth between the profiles.

For example, if you don’t need your eSIM profile while on vacation and have signed a prepaid contract with eSIM on site, you can deactivate your home profile and upload and switch on the profile of a network on site. Back at home, you deactivate the holiday profile and put the saved home profile back into operation. A data connection is not necessary for this, such a profile change takes place locally in the device.

However, only one profile can be active at the same time in an eSIM. Dual SIM devices therefore still require a physical SIM card in addition to the eSIM. Theoretically, this would also work with two eSIMs, but no device with this kind of equipment has yet been on the market. With two eSIMs you would have to make sure to install the downloaded profiles on the correct eSIM, because if you want to use two profiles at the same time, they have to be installed on different eSIMs.

The online function of the electronic ID card for smartphones (eID), whose data can be securely stored on the eSIM, could boost interest. The app, which Vodafone, Giesecke + Devrient and Bundesdruckerei are currently developing in cooperation, is due to start in autumn. The technology would also enable further authentication functions via the eSIM, such as an electronic driver’s license or tokens for locking systems.

The mobile phone providers apparently understand the eSIM as a premium function and not as a logical further development of the previous cards. An eSIM is only available from O2 and Vodafone for contract customers. Only Telekom also offers it for prepaid customers.

At O2 and Vodafone, new customers must first order a physical SIM card before adding an eSIM to the existing contract. There are probably organizational reasons for this: When the SIM card is sent, the provider checks that the address provided is correct and that the contractual partner receives his mail there. Telekom is proceeding more efficiently. Here the customer can select an eSIM when ordering and download it after identification.

With its mobile phone brand Simquadrat, Sipgate is targeting the new technical possibilities. Customers can order an eSIM there directly and install the profile on their device immediately after identification. Existing customers can switch between physical SIM and eSIM at Simquadrat at any time; the code printed on the SIM card serves as a security feature. The provider Truphone, which offers an international data tariff, relies exclusively on eSIMs. It is ideal for testing the eSIM function, the first 100 megabytes are free.

An eSIM can be activated in different ways. If the device has a camera, the easiest way to do this is to use a QR code, which the system reads in from the screen or from a letter when setting up the eSIM. Alternatively, the included activation code can be entered manually. Some providers also secure this process with an ePIN, which is sometimes also referred to as a confirmation code. Alternatively, an app from the mobile network provider downloads and installs the eSIM profile. It works differently if the device does not have a keyboard, for example a smartwatch. An app then usually requests the eSIM profile on a connected smartphone and transfers the data to the watch.

The activation code for the eSIM profile contained in the QR code can also be entered manually if necessary.

The eSIM profile can also be transferred via the settings at the provider. To do this, you have to store the device’s eID, the unique identification number for the built-in eSIM. Then you start the download of the profile via the menu of the device. The eID can be read out in the device settings. However, this is not convenient: The eID has 32 characters.

The eSIM significantly simplifies the handling of SIM cards and makes it easier for the user to change his device or mobile network provider. ESIMs are still only available in upper-class smartphones, and many providers are still not offering eSIM to their prepaid users. Like other convenience features, the eSIM will soon also be found in mid-range devices.

And the possibilities of the eSIM are not limited to mobile phone access; numerous other possible uses are conceivable, such as the electronic identity card. In the future, customers will naturally expect to be provided with the appropriate eSIM profile for their devices upon request. And then the plastic SIM has had its day.

In c’t 12/2021 we are dedicated to the brand new Disinfec’t 2021 with four virus scanners including one year of free signature updates. We explore exciting smartphone apps for forays into nature and have tested boards for Core i-1000, external SSDs for data transport, video lights for the home office and smart displays for Alexa & Co. You will find issue 12/2021 from May 21st in Heise shop and at the well-stocked newspaper kiosk.


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