From Walkie-Talkies to eSIM: How Mobile Communication Evolved

We have long been used to having cameras and audio players in our smartphones, paying with our phones, and keeping documents in apps. Things that once required separate devices or cards now fit into a single smartphone.

Against that backdrop, the plastic SIM card long remained a strange exception. You still had to insert it into a slot, move it when switching to a new phone, take it out while traveling, and keep it safe, because losing it could also mean losing access to your number.

eSIM changes this pattern. It does not remove the basic function of a SIM: your smartphone still needs to identify you as a subscriber and know which network to connect you to. But instead of a removable card, it uses a built-in module, while the operator profile is downloaded remotely.

This is the principle behind modern eSIM services like Yesim: users choose a mobile plan online, install the profile on their smartphone, and connect to a network without a physical SIM card.

This is not a sudden leap or a technology of the future. It is more like the logical outcome of a long story: devices became smaller, internal space became more valuable, and the familiar piece of plastic gradually turned into a service.

Before SIM cards, mobile phones were tied to the device

To understand how we got here, it helps to look back. Before the mobile phone as we know it, there were walkie-talkies, in-car communication systems, and bulky portable phones. But something you could simply put in your pocket and carry with you every day was still a long way off.

In the 1920s, some American police departments began using radio-based phone communication. It was used to transmit information about crimes and suspects to receivers in patrol cars. Following the police, taxi services in Detroit began using similar technology: drivers could switch to specific channels to communicate with dispatchers.

It soon became clear that the technology could go further.

In 1973, Martin Cooper, one of Motorola’s lead engineers, introduced the world to the first portable mobile phone. Later, in the 1980s, the Motorola DynaTAC 8000X became one of the symbols of early mobile communication. It weighed about 790 grams, offered around 30 minutes of talk time on a single charge, took about 10 hours to recharge, and cost nearly $4,000.

By today’s standards, it was a real dinosaur. But at the time, the very possibility of making a call wirelessly already felt like a technological breakthrough.

Still, those phones had one major drawback. They did not yet have SIM cards in the sense we know them today. The phone number and network access were tied to the handset itself. In other words, if you bought a new phone, you could not simply move a card to the new device and keep using the same number. You had to contact the operator to transfer the service to the new device.

The industry needed a way to separate the user from the device.

SIM made mobile identity portable

The SIM card became that solution.

SIM stands for Subscriber Identity Module. This is an important point: a SIM was never just a piece of plastic. The plastic was just the casing. Inside was a secure chip that helped the network identify the subscriber connecting to the operator’s services.

The first commercial SIM cards appeared in 1991. They were produced by Giesecke+Devrient for the Finnish operator Radiolinja, later known as Elisa. They were roughly the size of a bank card.

For its time, that format made perfect sense. Phones were still large, and there was enough space inside the casing for a big card. What mattered most was not the size, but the idea itself: subscriber data could now be stored separately from the device.

The phone number and network access were no longer strictly tied to a specific device. The SIM could be removed and inserted into another phone. Today, this seems obvious, but for mobile communication it was an important shift: switching to a new phone became much easier.

As phones got smaller, SIM cards had to shrink too

Then the idea of what a mobile device should be began to change.

The phone was gradually becoming more than just a tool for communication. Manufacturers were increasingly trying to turn it into a pocket computer with a calendar, email, notes, internet access, and other functions that had previously been tied to separate gadgets. IBM, Nokia, and Palm all experimented with this concept. Devices such as the Nokia Communicator and Palm Treo already showed where things were heading: the phone was no longer just a handset for calls, but a personal digital assistant.

But this idea truly became mainstream with the arrival of the iPhone and Android smartphones. The touchscreen, apps, mobile internet, and an ecosystem of services changed user expectations. A phone now had to do more than make calls: it had to take photos, store documents, show maps, handle payments, entertain, and help people work.

And the more tasks were packed into a single device, the more valuable internal space became. Manufacturers had to fit more hardware into one compact casing, and every millimeter started to matter.

The SIM card began to shrink too.

First, the full-size format gave way to the more compact mini-SIM, which long remained the standard for regular mobile phones. Then came micro-SIM, which became especially prominent after the release of the iPhone 4. Apple did not create these standards on its own, but the iPhone noticeably accelerated the shift to smaller formats: after the iPhone 4, operators began issuing micro-SIM cards on a large scale, and then the iPhone 5 made nano-SIM familiar across a new generation of smartphones.

Each new size reflected the same trend: technology was becoming more complex, while the physical medium used to connect to a network had to take up less and less space.

This was not just a design choice. A smaller SIM gave engineers more room for the components that shaped the next generation of smartphones: larger batteries, better cameras, additional sensors, antennas, and denser internal layouts. And removing the slot itself meant fewer openings and moving parts in the casing, making the phone easier to protect against water and dust.

Nano-SIM was almost the physical limit

By the early 2010s, SIM cards had almost reached the smallest practical size.

In 2012, ETSI standardized the 4FF format, known as nano-SIM. It measured 12.3 × 8.8 mm and was 0.67 mm thick.

By that point, it had become clear that there was almost nothing left to shrink. The card was already tiny. There was very little plastic left around the chip, and the format had come close to its physical limit. Manufacturers could have kept fighting for fractions of a millimeter, but that would not solve the main problem: users still had to insert the SIM into a slot, take it out, swap it, and keep it safe.

So the next step was not to make the card even smaller. The more logical step was to eliminate the need for a removable SIM altogether.

What eSIM actually is

eSIM is often called an “electronic SIM card,” but that is not entirely accurate. The “e” actually stands for embedded.

It is not an app, and it is not just a QR code. eSIM is a microchip inside the device. It performs the same basic task as a traditional SIM: it helps the device connect to a mobile network and verifies that the user is authorized to use a specific plan or operator profile.

The difference is that users no longer insert a card manually. Instead, a digital profile is downloaded to the smartphone. It contains the data needed to access the network: operator details, service settings, and in some cases, a phone number.

From the user’s perspective, the process is simple: choose a mobile plan, scan a QR code or install the profile through an app, and then select the eSIM in the phone’s settings, either for mobile data or as an additional line.

In other words, the SIM as a function does not disappear. Only the plastic card does.

Why travelers notice the difference first

For travelers, this shift is especially noticeable.

A trip often used to mean a separate set of steps: find a carrier store, buy a local SIM, remove your own SIM, make sure not to lose it, insert the new one, and check whether the internet works. Sometimes everything went quickly. Sometimes you have to deal with language barriers, documents, APN settings, and plan restrictions.

Yesim, a Swiss eSIM provider, offers a clear example of how this scenario works in practice. Users choose a country or region and select the option that fits their trip: a fixed data plan, an unlimited plan, a global package, or pay-as-you-go. Instead of looking for a local SIM after arrival, users can install an eSIM in advance and choose a plan for the trip they are taking: a short city break, a long vacation, or a route across several countries.

This is especially convenient for people who frequently travel between countries, work remotely, or do not want to depend on roaming. One device can store several eSIM profiles, and users can switch between them in the settings.

There is also a more practical everyday benefit: fewer small things that are easy to lose. You do not need to look for a SIM ejector tool, keep an old card in your wallet, or worry that it might fall out somewhere at the airport.

Is eSIM safer than a physical SIM?

eSIM has another important advantage: security.

An eSIM profile is stored not on a removable card, but in the eUICC – a built-in secure module inside the smartphone. This makes the profile harder to steal, copy, or transfer to another device without the owner’s knowledge.

Installation does not work like a simple file download from the internet either. eSIM uses Remote SIM Provisioning, a GSMA standard for remotely downloading and managing profiles. In this system, the profile is delivered to the device through a secure channel and installed in a dedicated area, rather than simply saved in the smartphone’s memory.

This is also useful when traveling. If mobile internet is already set up, there are fewer reasons to connect to random open Wi-Fi networks in airports, cafés, or hotels.

The basic rules still apply: protect your account, do not click suspicious links, and install eSIM profiles only through trusted providers. So eSIM is better understood not as absolute protection, but as a more modern and more secure way to connect.

From object to service

At first, mobile connectivity was tied to large devices and complex infrastructure. Then the phone became personal. The SIM card separated the subscriber from a specific device and gave users more freedom. Later, the card itself began to shrink: from a bank-card-sized format to nano-SIM.

eSIM follows the same path. It does not change the basic logic of mobile connectivity, but makes it more convenient for users. The real evolution here is not that SIM became more stylish or more advanced-looking. It became less visible to users.

Good technology stays inside the device, works in the background, and does not require extra steps.

The SIM card has gone from a bank-card-sized piece of plastic to a profile that can be downloaded to a smartphone. eSIM is not a sudden replacement for an old technology, but the logical endpoint of its miniaturization: when the card can no longer be made much smaller, it stops being a card.

If you want to try eSIM on your next trip, start with the basics: check whether your device is compatible, download the Yesim app, and use promo code GETYESIM to get 15% off.