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What is a SIM card? Advantages, compatibility, and more

Read all the information about what a SIM card is, learn about its advantages, how it works, types of SIM, and more!


July 26, 2023

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You are probably wondering what a SIM card is. That’s why we prepared this article, where we will tell you all about this way to connect to the internet and stay in contact. We will tell you about the advantages, sizes and types, compatibility with iPhone or Android devices, and where to get one.

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What is a SIM card, and why should I get one?

The SIM card is a removable plastic card used in mobile devices (tablets, USB modems, cellphones, and smartwatches). It is used to store a subscriber’s service key to authenticate and securely access a specific telecommunications network.

With this information, the user will be able to use the contracted mobile services (internet, SMS, and calls) for local or international use. Also, the physical SIM is used as a storage medium. Telephone contacts and text messages are stored. This way, the user can access them from any other mobile device.

The SIM card that we know now has been changing, and it has currently removed the use of plastic cards. It has been replaced with virtual SIM cards. They are already integrated into the motherboard of cell phones compatible with this new technology.

SIM card formats and sizes

The SIM card has changed a lot over time. This is thanks to the interest of its manufacturers in finding smaller and smaller sizes. This favors the design and appearance of mobile devices, thanks to space savings and the possibilities of expanding their storage.

Different types of SIM cards
Types of SIM cards. Source: A1 Bulgaria

We list the various SIM card types in the following table, which are easy to distinguish by their format and size.

Type of SIM cardSize
Traditional SIM85.6mm x 54mm
Mini-SIM25mm x 15mm
Micro-SIM15mm x 12mm
Nano-SIM12.3mm x 8.8mm
Virtual SIM (eSIM)6mm x 5mm
Table 1: Various SIM card sizes.

The first SIM card was as big as a credit card and was used on analog mobile phones. Its later versions: Mini, Micro, Nano, and Virtual SIM, were adapted to smartphones, from their appearance at the end of the 1990s up to the present day.

There is no doubt that the SIM card changes have brought multiple benefits for manufacturers of iPhone and Android devices. The most important has to do with the possibility of improving the user experience with increasingly compact and functional designs.

SIM Card compatibility on iPhone and Android mobiles

The compatibility of a SIM Card in different iPhone and Android models can be easily identified, considering the format and size supported by each device, as shown in the following table with the most popular devices:

iPhone and Android modelsType of SIM card
iPhone 4 and previous modelsMini-SIM
iPhone 4s to iPhone 6 PlusMicro-SIM
iPhone 6s to iPhone XNano-SIM
iPhone XR, XS, XS Max, iPhone 11, 11 Pro, 11 Pro MaxDual SIM, Nano-SIM, and eSIM card
iPhone SE (2020) and more recent modelsDual SIM, Nano-SIM, and eSIM cards
Android devices prior to 2011Mini-SIM
Android devices from 2011 to 2012Nano-SIM
More recent Android devicesNano-SIM / eSIM card
Table 2: SIM card compatibility according to the phone model

Compatibility also has to do with the geographic region and the operator. We recommend you verify this information before making any purchase decision, especially in other countries.

For example, the iPhone 14 in the United States already comes without a slot for a removable SIM Card. In other countries, this same model is dual-sim and accepts conventional SIM Cards as eSIM cards. It would be more practical to have this device and not the one you bought abroad.

Advantages of using a SIM Card

The advantages of having a SIM Card are many, but we can summarize them in terms of portability. Which lets users keep their personal information, such as personal data and contacts. This card allows the manual transfer of information between devices.

Also, it is an alternative that allows access to mobile services anywhere where the GSM mobile network is covered. And because of the power of adaptation to satisfy each one of the user’s needs, just as it happens with travelers when it comes to finding cheap alternatives to communicate abroad with a local or international SIM.

Where to get a SIM Card?

Nowadays, there are many ways to obtain a SIM Card, and it is very simple. You just have to pick the mobile cellphone company you prefer or an authorized point of sale near your location and request the SIM Card. Each country has a list of mobile operators, such as Orange, Vodafone, Movistar, Claro, Telcel, AT&T, Verizon, T-Mobile, and many others.

You can also get a SIM Card from an internet provider or e-commerce stores. Some examples are Amazon, eBay, and MercadoLibre, following the steps to make the purchase online.

Below, we are going to tell you about the different ways to acquire one.

Buy a SIM card online

With this option, it doesn’t matter whether you are in a foreign country or at home, you can get a SIM card anywhere you are. You only need to visit a mobile operator’s virtual store or a specialized provider to get your SIM with the data plan you choose.

In this case, you can choose a virtual SIM card that works without a plastic card. You’ll receive it in a few minutes, right after the purchase is confirmed. Or, if you prefer, you can buy a plastic card, but you will have to wait a few days to receive it through the mail service.

Buy a SIM card in physical stores

Buying a SIM card in a physical store is very practical, except if you are in countries with cultures and languages that are very different from those of your country. Nonetheless, the stores of the operators and authorized points of sale are always located in strategic places in the city. For example, airports, shopping centers, supermarkets, and technology stores.

Different mobile operators
Different mobile operators. Source:

Consider that to get one of these chips with an operator, you will have to consider the opening and closing hours of the stores you plan to visit so that you do not waste time. Make sure you bring the necessary documentation to meet the purchase and activation requirements of a SIM.

Conclusions about what is a SIM card

After all this information, we can mention that the SIM Card is the universal name used to identify the card (virtual or physical). This is the chip used in mobile devices (tablets, USB modems, watches, and smartphones). Here, the service key that identifies you internationally, is stored, and lets you connect to a certain telecommunications network.

Thanks to its existence, anyone has the possibility of communicating via the Internet, analog calls, or text messages in any place where there is coverage, through compatible mobile devices. They also have the possibility of storing information and passing it manually from one device to another without complications.

Its evolution has made it possible to find alternatives with smaller sizes that favor the design, manufacture, and sale of smartphone devices, significantly improving the user experience, as is the case with the international virtual SIM.

Frequent questions about SIM cards

Why does it say invalid SIM card?

An invalid SIM card error can happen because the SIM has not been inserted correctly into the mobile device. Or because the user used a chip from another mobile operator on a device that the operator had blocked.

What does it mean that there is no longer a SIM card on the mobile?

It may refer to the fact that there are mobile devices that will soon no longer have a slot to insert or remove a physical SIM card. The main mobile carriers in the United States are doing this with the iPhone 14.

How many SIM cards can be used on a cellphone?

The answer depends on the cellphone model and its compatibility with the different formats of SIM technology. Some devices accept SIM, Dual SIM, eSIM, and soon iSIM.