[The Era of 1 Phone 2 Numbers③] Originally, SIM Cards Were for Set-Top Boxes... The History of SIM Cards

Over 20 Years of Mobile Phone Evolution
Miniaturization of SIM Card Sizes
Initially Installed in Set-Top Boxes
Equipped in Mobile Phones Since 2G Era
E-SIM Evolved into a Virtual SIM Card

A SIM card is a 'Subscriber Identity Module device' that contains the identification information of line subscribers.

[Asia Economy Reporter Cha Min-young] The 'SIM card,' a 'mobile ID' for cellphone users, has undergone numerous external changes over the past 20 years alongside the evolution of mobile phones. Initially created to identify set-top box users, it was credit card-sized, but its size decreased as it began to be used in mobile phones. With the advent of the smartphone era and the increasing number of components inside phones, the SIM card continued to shrink. Eventually, with the birth of the eSIM (embedded Subscriber Identity Module), the SIM card evolved into an intangible form without a physical shape.

Created to Identify Pay TV Subscribers

The SIM card, or Subscriber Identity Module device, contains identification information for line subscribers. It holds personal information and, despite its small size, provides storage space enough to save a phonebook. While SIM cards are commonly associated with smartphones, the early full-size SIM cards were developed for use in set-top boxes. The full-size SIM card is similar in size to a standard credit card. It was mainly used in early foreign GSM mobile phones developed in the 1990s, as well as IPTV set-top boxes, satellite boxes, and cable TV set-top boxes.

The SIM card, which was initially credit card-sized, has shrunk every year. As smartphones required more functions and internal space utilization became a concern, the SIM card's exterior was miniaturized. The size decreased from the original full-size SIM card to mini SIM, micro SIM, and then nano SIM, with thickness also becoming thinner. The nano SIM, the last physical SIM card before the eSIM, is 0.67mm thick, whereas the previous mini SIM was 0.76mm thick. Its height has also been reduced to 12.3mm, about half of the previous 25mm.

SIM Cards Used in Korea Starting from 3G Phones

SK Telecom YouTube capture

SIM cards have been included in smartphones since the 2G phone era. Overseas, GSM technology was adopted, so SIM cards were used from 2G phones. In Korea, however, the 2G mobile communication technology used the CDMA (Code Division Multiple Access) method, which did not require SIM cards. The CDMA method registered the subscriber identification code directly in the device by the mobile carrier. Therefore, while overseas users only needed to replace the SIM card when changing phones, Korean users had to visit the carrier to register a new device even when changing phones. This difference led to the formation of a separate mobile phone distribution market (now known as the unlocked phone market) in countries adopting GSM, whereas in Korea, mobile carriers began directly distributing phones.

With the dawn of the 3G era, SIM cards became widely used in Korea. The mini SIM form factor was introduced alongside the initial spread of SIM cards, opening the smartphone era. Starting with Apple's iPhone in 2007, followed by Google's 'Nexus One,' Samsung Electronics' 'Galaxy S,' and LG Electronics' 'Optimus Z,' all smartphones used mini SIM cards.

Getting Smaller and Smaller, Eventually Disappearing

The micro SIM was mainly used in late 3G smartphones and 4G (LTE) smartphones. It was a new standard introduced to reduce SIM card size as smartphone internal structures became more complex. Representative models include Apple's 'iPhone 4' from 2010, Google's 'Nexus 4,' Samsung Galaxy Note series, and LG Electronics' 'Optimus View' from the Optimus series. The nano SIM was mainly used in smartphones after the commercial launch of VoLTE. Smartphones produced between 2012 and 2016 adopted this smaller size. The eSIM, introduced from September 1, is embedded in devices such as Apple's 'iPhone XS' produced after 2017, Samsung Galaxy Watch, Google's Pixel 3 series, and Xiaomi smartphones. Samsung Electronics has also provided eSIMs in some overseas models.

At one time, physical SIM cards were cut to change their size. If the SIM card size did not fit, users would fill or cut it to fit. Conversely, to make a smaller SIM card larger, a 'SIM card adapter' can be used. By simply inserting the SIM card into the adapter, the size can be changed, allowing nano SIMs to be converted to micro or standard SIM sizes. SIM card adapters are sold on overseas sites like eBay, as well as on Korean open markets such as Coupang and Gmarket, and even at stores like Daiso.