What is a SIM Card and How Does it Work


If you have a phone, chances are that it has a SIM card. This card is simply known as the Subscriber Identity Module. Unlike other components found in your phone, this one is small in size and stores a lot of information about a mobile phone user. Besides the user’s ID, this portable memory chip contains a 7-digit code that shows the country of origin and the carrier to that it is connected.

With a SIM card, you will be able to connect to your carrier’s network once you switch on your phone. It is imperative to note that these SIM cards come in a number of sizes and types. Since most people like to know more about SIM cards, we shall take a closer look at that, their history, and types, alongside other related facets.

History of SIM Cards

SIM cards have come a long way. To start with, they were introduced in 1991. In fact, the first SIM card resembles a credit card. Over time, they underwent a couple of changes and updates and now look smaller in size.

Interestingly, SIM technologies such as GSM is related to SIM cards as they rely on this technology in order to function well. GSM refers to the Global System of Mobile Communications. It is basically the standard network in continents such as Africa, Asia, and Europe. Other places usually rely on SIM technologies such as CDMA (Code Division Multiple Access).

The latter is very prominent in the United States. In fact, carriers such as Sprint and Verizon support CDMA phones. Thankfully, we have phones that support both GSM and CDMA. Finally, the SIM card acts as the brain of your mobile phone as it allows it to connect to your carrier’s network.

Types of SIM Cards

Depending on your phone, there are different sizes of SIM cards that you can insert and get connected to your carrier’s network. When it comes to SIM card sizes, you can expect to find an array of them out there in the market. Some are small while others are large in size. As we speak, you can expect to find the following SIM card sizes once you go to the market:

eSIM and Soft SIM

Unlike the conventional SIM cards mentioned above, this one is quite new in the market. As the name suggests, this one is usually embedded directly on a mobile phone. Therefore, it is very difficult to remove it.

Compared to other SIM cards, this one is not commonly used out there. It, however, gives phone users the luxury to swap phones without essentially having to transfer SIM cards. Here, your carrier of choice will transfer the details of your account remotely. Therefore, you can readily swap these phones from the comfort of your home and enjoy more convenience.


Compared to the SIM cards we have outlined above, this one is the smallest one in size. This is because the SIM card measures 12.3 mm by 8.8 mm in size. As a result, it has the smallest contact surface and thus not ideal for older phone models. This is because such models need a Micro-SIM card instead.


The above-mentioned SIM card resembles the Mini-SIM due to the nature of its contact surface. Its contact surface, however, is relatively smaller in size as it measures 15mm by 12mm. Unlike the Mini-SIM, Micro-SIM’s plastic segment is trimmed a bit, thereby leaving the SIM card with the contact surface only.


Since the full-size SIM cards were phased out, mini-SIM cards are now deemed to be the standard or full SIM cards. It is imperative to note these cards measure 25mm by 15 mm. Their contact surface is usually surrounded by a plastic segment that is large in size.

Full-size SIM

As the name suggests, this SIM card used to be very large. As we mentioned above, they resembled credit card. To put this into perspective, they used to measure 86mm by 54 mm.

Although these SIM cards used to be large in size, their actual contact surface was still small in size. In fact, its contact surface resembled the same as those of contemporary SIM cards. Although these SIM cards were a lifesaver in the 1990s, they are no longer in use as we have newer versions in the market.

Can You Use a Phone without a SIM Card?

Yes. As we speak, you can use your phone without inserting a SIM card. You will, however not have the privilege to use a number of functionalities on your phone like making calls. Additionally, you will not be able to send messages to your friends and family.

Unless you connect your phone to a Wi-Fi network and use messaging apps such as WhatsApp, you may not be able to use your phone to communicate with those whom you love. You can however take photos and use the calculator feature of your phone even when it does not have a SIM card.

Is it Worth Getting a Dual-SIM Phone?

Yes. If you want to enjoy flexibility in terms of swapping carriers, there is a need for you to invest in such a phone. Here, you can choose one SIM for one carrier and the other one for another one. In fact, you will be at liberty to use two SIM Cards of different carriers at the same time.

Better still, you can use the different SIM cards of the same carrier on your phones and take advantage of any existing deal. Either way, the flexibility that comes with dual-SIM phones is unmatched.

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