What is A SIM Card? How Does It Work?

Haseeb Awan
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July 20, 2022
Modified On
April 5, 2023

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Modified On
April 5, 2023

Consider your phone is the body, and its SIM card is its soul. Just like the body won't function without the soul, you must first register it with a mobile phone network to use it to make and receive calls, send SMS, and more.

To initiate phone conversations and send messages, the majority of mobile phones use a small card known as a SIM card. Without it, your smartphone can only access the internet but cannot connect to the mobile network.

This blog will discuss a SIM card, how it works, and answer the FAQs about SIM cards. Continue reading.

What Is A SIM Card?

SIM stands for Subscriber Identity Module. A SIM card is a little smart card uniquely identifiable to a particular mobile phone network. With this card, users can make and receive phone calls, send Text messages, and access cellular internet services using their smartphones.

It is worth noting that even though SIM cards' sizes have evolved since they were first created in 1991, their capability has not. Operators can determine your location based on the SIM card, the networks you've connected to, and your SIM card ID, which serves as your network Address.

All smartphones on GSM and CDMA networks have SIM cards inserted. Most carriers worldwide, including T-Mobile and AT&T in the United States, operate on GSM networks, while Sprint and Verizon operate on CDMA networks.

SIM Cards Types

As discussed earlier, SIM cards have been modified in size, but their functionality has stayed the same. So, here are the types of SIM cards based on their sizes:

  1. Complete SIM: This version is no longer in use. It was the original version of the SIM card when it was first introduced in the 1990s. Its size was 86x54mm.
  2. Mini-SIM: Mini SIM card is 25x15mm and is considered a full-size card.  
  3. Micro-SIM: A micro-SIM is further smaller with a size of 15x12mm. 
  4. Nano-SIM: As evident by its name, the Nano SIM card is the smallest in size at 12.3x8.8mm. It is the most frequently used SIM card today.
  5. eSIM: eSIM (Embedded SIM) is a brand-new, developing format where the SIM is permanently integrated into the gadget and is irremovable. Despite its rarity, the benefit of an eSIM is that it lets you switch smartphones without changing SIM cards because the phone carrier does so remotely.
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How Does A SIM Card Work?

SIM cards identify which accounts are connected to which phones by informing the telecom operator which account belongs to which device. Typically, network operator providers refer to their clients as "subscribers." The client card, known as a SIM, enables your smartphone to access the network.

How to Install A SIM Card?

Inserting the SIM card is simple once you have the SIM card and know about the SIM slot on your phone. Every size of SIM card requires the exact same procedure. To remove the SIM tray, start by turning off your phone. Then, locate the little hole on the side of the device and insert the tool or a paperclip. Put the tray back in with caution, then turn on the phone.

How to Remove A SIM Card?

Although SIM cards come in various sizes, they always function the same way and are made to be simply swapped between smartphones. If you've lost the small SIM card extractor that came with your device (it resembles a small pin), you might use a tiny paperclip instead. Locate the SIM tray on the side of your smartphone, and then push a clip or SIM tool into the gap to release the tray.

How to Change the Network of the SIM Card?

As mentioned earlier, GSM and CDMA as the two leading networks in the United States. You could theoretically remove your T-Mobile SIM card, insert it into an AT&T-compatible handset, and resume using your smartphone on the T-Mobile network after notifying them of the transition if you are on a GSM network like T-Mobile or AT&T.

Unfortunately, switching from a T-mobile-enabled cellphone to Verizon, which uses CDMA, won't be easy. However, to make it function, you will need to have a CDMA SIM card authorized by Verizon.

Fortunately, many of the most well-liked cellphones available today, like Apple's most recent iPhones, have complete compatibility with GSM and CDMA networks. As a result, moving your device between networks is simple.

Can SIM Cards Pose A Threat to Your Security?

SIM cards are not invincible to hackers, who are pervasive. Because it holds your contact number, which is often connected to your bank, emails, corporate profiles, and social media accounts, your SIM card is a top target for attackers. Cybercriminals can contact a cell phone provider and pose as you to swap your phone number to their SIM card. After doing that, they can copy all of your personal information to a new SIM card, insert it into their smartphone, and exploit you.

The ability to reset passwords via text message makes it simple for scammers to access your financial, email, and social media accounts.

Have you noticed you are out of signals and not receiving phone calls or messages? Try ringing your phone; if it does not ring, it might mean your SIM has been compromised. Reach your mobile network provider as soon as possible to fix the issue.

Read more about A SIM Swap Attack and Its Prevention Techniques.

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Haseeb Awan
CEO, Efani Secure Mobile

I founded Efani after being Sim Swapped 4 times. I am an experienced CEO with a demonstrated history of working in the crypto and cybersecurity industry. I provide Secure Mobile Service for influential people to protect them against SIM Swaps, eavesdropping, location tracking, and other mobile security threats. I've been covered in New York Times, The Wall Street Journal, Mashable, Hulu, Nasdaq, Netflix, Techcrunch, Coindesk, etc. Contact me at 855-55-EFANI or haseebawan@efani.com for a confidential assessment to see if we're the right fit!

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