What is Stored on a SIM Card? [All You Need To Know]

Your phone has died and now need to take out that small thingy with a chip and put it on another phone. That tiny bit of plastic you’re transferring is your SIM card.

If you want to find out how it works and what is stored on a SIM card, read on.

But, first:

What Is a SIM Card?

The full name of the SIM card - Subscriber Identity Module - reveals what it actually is. To mobile networks, we are all subscribers. They use SIM cards to identify our phones and the activities we perform on them.

So, the portable memory chip you’ve taken out of your device is the ID card of your phone. It contains printed integrated circuits with a seventeen-digit number. This code is unique. It designates the country, carrier, and user of any mobile phone.

There is also a variety of information on the SIM card such as who is paying for the access and the permission to use the features like making and receiving a call or a text message. 

How Does a SIM Card Work?

Insert the SIM card in its designated slot, wait for the phone to connect to a mobile network and you are good to go! Of course, you need to see first if the carrier identifies whether your phone can operate on their network. This is basically what SIM cards are used for.

In many countries, mobile companies lock their SIM cards and devices. So, if you purchase your phone and SIM card from the same carrier you have access to all features. If not, you can’t place any calls or send any texts on the network except emergency calls. It’s possible to unlock your cell with permission from the cellular operator.

SIM cards are also important to mobile providers. Besides its primary SIM card function to identify its users and route calls, phone companies track your phone usage. The minutes, texts, and data utilization are measured so that carriers can charge you for their services. They can also turn them off if you don’t pay your bills. Hence, you can have a SIM card properly placed but your phone won’t work.

What Is Stored on a SIM Card?

SIM cards can save only a certain number of your contacts and some text messages. But, there is more to it.

Here is the other information stored on your SIM card:

• Integrated Circuit Card ID or ICCID - unique serial number containing 19 or 20 digits typically printed on the back. It identifies the SIM card itself.
• International Mobile Subscriber Identity or IMSI - number used to uniquely identify the individual operator’s network. The number of digits varies but is usually around 15.
• Mobile Country Code or MCC - the first three digits of IMSI that identify the region the mobile subscriber belongs to.
• Mobile Network Code or MNC - the next two digits of IMSI (for Europe) or three digits (for North America); they identify the home public land mobile network displayed when a mobile user is connected to a network.
• Mobile Subscription Identification Number (MSID) - the remaining digits identify the mobile subscriber to a network.
• Authentication key (Ki) - SIM card details used for its authentication on a mobile network.
• Local Area Identity - the unique number of the operator network’s location area.
• Service Provider - the name of your mobile operator.
• Service Dialing Numbers - used for information about the services such as your current balance.
• Advice of Charge (AoC) - estimation of the costs of individual ongoing calls.
• Short Message Service System - enables your text messaging.
• Unblocking code (PUK) - used to unlock your phone if you keep putting in the wrong PIN (Personal Identification Number).
• Voice-added Services - any additional services for your purchased phone.

This seems like a lot of information and you’re probably asking yourself:

How Much Data Is on Your SIM Card?

SIM card storage capacities are not that big and usually range from 8KB to 256KB or 512KB for newer cards. The SIM card contains your key data plus around 250 contacts and some messages.

However, you can’t use it as a memory bank. If you need extra space you need to install a micro-SD card (if it’s supported on your phone).

How to Check What’s on Your SIM Card?

To see SIM card data on your Android phone, go to Settings and tap “About phone”. You can also search “About phone” and then choose “Status” and “SIM status” to see your network, roaming info, signal strength, and more.

On an iPhone, you can go to Settings, then choose “Cellular” and “Celular Data Option” to see info on your SIM card. There is also an option to see if any apps are using storage on your SIM card by choosing SIM Applications in Settings.

If you want to see precisely what’s on your card, you can even buy a SIM card reader. That’s a separate piece of hardware used for transferring SIM card info to your computer for further inspection.

Can Your SIM Card Get Hacked?

Your SIM card is not immune to hacker attacks. An average person uses a SIM card to place and receive calls and send text messages. Then, you might ask yourself, why do fraudsters need it? They are after your phone number which is often linked to your email, social media accounts, and banking details.

There isn’t one, but three different ways to get your SIM card hacked:

SIM Cloning

One way to compromise your SIM card is to clone it. For this hack, someone has to have physical access to your original card. They use smart card copying software to transfer all your SIM card data onto a duplicate. With it, they can make calls and send messages in your name.

SIM Jacking

Cybercriminals can also send a spyware-type code to your phone in a text message. When you open it, the hacker gets access to your calls and messages. They can utilize your phone apps and see your passwords which they can later change to new ones. Your bank account is the first target on their list.

SIM Card Hijacking

This is another way cybercriminals pretend to be you. They call your cell phone operator convincing them to change the SIM. Then they transfer your SIM card details to another card, getting access to your text messages. Fraudsters can reset passwords through a text message and your bank account is once again at high risk. 

Wrap Up

Well, now you know what information your SIM card contains and what it is used for. 

SIM cards might be a 30-year-old technology but they are here to stay.

For how long? We’ll see.