What Information Is Stored on a SIM Card?

A SIM card, or Subscriber Identity Module, is a small yet powerful microchip that plays a crucial role in connecting your mobile phone to a network. Whether you're making calls, sending text messages, or accessing the internet via mobile data, your SIM card acts as your digital identity within your carrier's system.

While most people are familiar with swapping SIM cards between phones, few truly understand the kind of information stored on them. 

Unlike your phone's internal memory, which holds apps, photos, and videos, a SIM card contains specific network-related data and user authentication credentials that help your carrier recognize you.

This article explores, in detail, the different types of data stored on a SIM card, their significance, and how they impact your mobile experience. Additionally, we’ll discuss the evolution of SIM cards, their limitations, and the future of SIM technology, including the rise of eSIMs.

1. Unique Identification Numbers and Network Information

One of the most fundamental roles of a SIM card is to store unique identification numbers that allow mobile networks to recognize and authenticate the user. These identifiers are critical for ensuring that your device can connect to the network securely and efficiently.

IMSI (International Mobile Subscriber Identity)

The IMSI is a unique 15-digit number assigned to each SIM card. It consists of:

• Mobile Country Code (MCC) – A 3-digit number identifying the country of the mobile network.
• Mobile Network Code (MNC) – A 2- or 3-digit number identifying the specific carrier within that country.
• Mobile Subscriber Identification Number (MSIN) – A unique number assigned to the individual subscriber.

Every time your phone connects to the network, it transmits the IMSI to verify your identity. However, to improve security, modern networks use temporary mobile subscriber identities (TMSI) instead of directly transmitting the IMSI to prevent tracking and fraud. This ensures that your identity remains protected even if the communication is intercepted.

ICCID (Integrated Circuit Card Identifier)

The ICCID is a globally unique 19- or 20-digit number that identifies a specific SIM card. Unlike the IMSI, which identifies the user, the ICCID is linked to the physical SIM card itself. This number is useful for carriers when activating or deactivating SIM cards and during number porting (transferring a phone number between carriers). The ICCID is typically printed on the SIM card itself and can be accessed through your phone’s settings.

2. Network Authentication Keys

Your SIM card also contains encryption keys that allow your phone to securely communicate with the network and prevent unauthorized access. These keys are essential for maintaining the integrity and confidentiality of your communications.

Ki (Authentication Key)

The Ki (Key Identifier) is a 128-bit secret key that ensures secure communication between your SIM and the carrier's network. Every time your phone connects to the network, a challenge-response authentication occurs:

1. The network sends a random number to your SIM.
2. Your SIM uses the Ki to generate a response.
3. The network verifies the response before granting access.

Since the Ki is stored in both the SIM card and the carrier’s database, it cannot be easily extracted, ensuring a high level of security. This process prevents unauthorized users from cloning your SIM card or accessing your network.

3. Phone Number and Mobile Subscription Details

MSISDN (Mobile Station International Subscriber Directory Number)

While your phone number isn’t physically stored on the SIM card, the SIM is associated with an MSISDN, which links your mobile number to the network. When you insert your SIM card into another phone, your phone number remains the same because the SIM is still linked to your carrier's records. This is why you can switch phones without losing your number.

4. Contacts (If Stored on SIM)

In the past, mobile users stored contacts on their SIM cards to easily transfer them between phones. Most modern smartphones now store contacts in cloud services (Google, iCloud) or in the phone’s internal storage. However, if a SIM card is used to store contacts, it typically supports up to 250 entries, containing only names and phone numbers—not additional information like email addresses, birthdays, or profile pictures. This limitation makes SIM-based contact storage less practical in today’s world of rich contact data.

5. Text Messages (Limited Storage Capacity)

A SIM card can store SMS (Short Message Service) messages, but the capacity is limited. Older SIM cards could store between 10 and 50 messages, while newer versions can hold up to 500 messages. Unlike phone storage, SIM-stored messages do not support advanced features such as emojis, multimedia, or group chats. Since most modern devices now save messages on the phone’s memory or cloud storage, SIM storage for SMS is rarely used.

6. Mobile Data and Internet Configuration

APN (Access Point Name) Settings

A SIM card also stores APN (Access Point Name) settings, which tell your phone how to connect to the internet using mobile data. APN settings include information such as:

• The gateway between the mobile network and the internet.
• The IP address your carrier assigns to your device.
• Whether your carrier uses private network settings or proxies.

Without these settings, your phone would not be able to access mobile internet or send multimedia messages (MMS). APN settings are particularly important when traveling internationally, as they ensure your phone can connect to local networks.

7. Roaming and Preferred Network List (PNL)

If you travel abroad, your SIM card stores a Preferred Network List (PNL), which determines which foreign carriers your phone can connect to. This is based on agreements between your home carrier and international networks. Your SIM scans for available networks and connects to the best option based on:

• Signal strength.
• Carrier agreements.
• Roaming charges.

This feature ensures seamless connectivity while minimizing costs and maintaining service quality.

8. Security and Protection Mechanisms

Your SIM card has built-in security measures to prevent unauthorized access.

PIN (Personal Identification Number)

A 4- to 8-digit security code that protects your SIM card from unauthorized use. If a PIN is enabled, the phone will ask for it every time it is restarted. This adds an extra layer of security, especially if your phone is lost or stolen.

PUK (Personal Unblocking Key)

If you enter the wrong PIN too many times, the SIM will lock. The PUK (Personal Unblocking Key) is a special code used to unlock it. If entered incorrectly too many times, the SIM may become permanently locked, requiring a replacement from your carrier.

9. Additional Features Stored on Some SIM Cards

Advice of Charge (AoC)

Some carriers store Advice of Charge (AoC) data, which allows users to check their usage costs in real time. This is particularly useful for prepaid users who want to monitor their spending.

Value-Added Services (VAS)

SIM cards may also store Value-Added Services (VAS), including:

• Mobile banking details (for some carrier-linked services).
• Carrier-specific features like voicemail settings.

10. Storage Capacity of SIM Cards

The amount of data stored on a SIM card depends on its generation:

• Older SIM cards had capacities between 8 KB and 64 KB, enough for contacts and SMS storage.
• Modern SIM cards can store up to 256 KB, but their primary role remains authentication, not data storage.

Since phone manufacturers and cloud services now provide ample storage, SIM storage is mainly used for network-related purposes.

What a SIM Card Does NOT Store

There are several misconceptions about what SIM cards store. A SIM does not hold:

• Photos or videos – These are saved on the phone’s internal storage or cloud.
• Installed apps or app data – Apps are stored in phone memory or cloud backups.
• Social media login details – Your Facebook, Instagram, or WhatsApp accounts are not stored on the SIM.
• Wi-Fi passwords – These are stored in the phone’s memory.

What happens if you take out your SIM card and put it in another phone?

If you remove your SIM card and insert it into another phone, your phone number, mobile network connection, and any contacts saved on the SIM card will move to the new phone.

However, not everything transfers. Your photos, apps, messages, and files will stay on your old phone because they are stored in the phone’s memory, not on the SIM card. If you want to transfer your photos, videos, and apps to the new phone, you will need to back them up using a cloud service like Google Drive or iCloud or transfer them manually.

If the new phone is locked to a different carrier, your SIM card may not work. In that case, you might need to unlock the phone or use a SIM from that carrier.

Can you see what information is stored on your SIM card?

Yes, but what you can see depends on your phone and whether the SIM card has been used to store information.

On Android phones, you can check SIM card details by going to Settings > About Phone > SIM status. This will show details like your phone number (if stored), network information, and signal strength. Some Android phones also allow you to view contacts stored on the SIM through the Contacts app.

On iPhones, SIM cards only store network-related data, so you won’t see much. To check basic SIM information, go to Settings > General > About, then scroll down to see the ICCID number, which is a unique identifier for the SIM card. iPhones do not allow you to store contacts or text messages on the SIM card, so you won’t be able to view anything else.

If you have an older phone, you may be able to see and edit contacts and text messages saved on the SIM through the phone’s Contacts or Messages app.

I lost my SIM card. What information can someone get from it?

Losing a SIM card can be worrying, but in most cases, the person who finds it cannot access your personal data such as photos, apps, emails, or social media. However, they may be able to access:

• Your phone number – If they insert the SIM into another phone, they could receive calls or texts meant for you.
• Contacts stored on the SIM – If you saved contacts directly to your SIM instead of your phone or cloud storage, they might be able to see those names and numbers.
• Text messages stored on the SIM – Some older SIM cards store text messages, but most modern smartphones save messages in the phone’s memory instead.

The biggest risk is if someone uses your SIM card to receive verification codes for two-factor authentication (2FA) on banking or social media accounts. This is why it is very important to call your mobile provider immediately if you lose your SIM card. They can block the lost SIM and issue you a new one with the same phone number, preventing anyone from using it.

Does removing a SIM card remove all data?

No, removing a SIM card does not delete anything from your phone. Your photos, videos, apps, and messages are stored on the phone’s internal memory or cloud storage, not on the SIM card.

When you remove the SIM card, your phone will still work, but you will not be able to make calls, send texts, or use mobile data unless you are connected to Wi-Fi. You can still:

• Take photos, watch videos, and use apps that don’t require a mobile network.
• Connect to Wi-Fi and use internet-based messaging and calling apps like WhatsApp, Facebook Messenger, and FaceTime.
• Access saved contacts, but only if they are stored in your phone’s memory or cloud, not on the SIM.

If you put the SIM back into the phone, everything will work normally again. If you replace it with a new SIM from a different carrier, your phone will need to be unlocked to accept the new SIM.

Can you delete all information stored on your SIM card?

Yes, but only certain types of information can be deleted from a SIM card.

• Contacts stored on the SIM – If your phone allows it, you can go to the Contacts app and manually delete any contacts saved on the SIM.
• Text messages stored on the SIM – If your phone stores SMS on the SIM, you can delete them just like regular text messages. However, most modern phones store messages in the phone’s memory instead of the SIM.
• Call logs – Call history is not stored on the SIM card, so deleting your call history from your phone will not affect the SIM.

Some information cannot be erased because it is programmed into the SIM by your mobile carrier. This includes:

• IMSI (International Mobile Subscriber Identity) – A unique number that identifies your SIM to the carrier.
• ICCID (Integrated Circuit Card Identifier) – The serial number of the SIM card.
• Network authentication keys – Security codes used to verify your identity with your carrier.

If you want to completely erase all data from a SIM card, the best way is to destroy it or request a new one from your carrier. You can also ask your carrier to deactivate the old SIM and issue a replacement with the same phone number.

Are eSIMs More Private Than Traditional SIM Cards?

Yes, eSIMs (embedded SIMs) are generally more private and secure than traditional physical SIM cards, but they still have some risks. Below is a detailed comparison of privacy and security aspects between eSIMs and traditional SIM cards to help you understand why eSIMs offer better protection.

1. Physical Security: eSIMs Cannot Be Stolen or Swapped Easily

One of the biggest risks with a traditional SIM card is SIM swapping. If someone steals your SIM card and inserts it into another phone, they can receive your calls and text messages, including two-factor authentication (2FA) codes for banking, social media, and email accounts.

With an eSIM, this is impossible because it is built into your phone’s hardware. There is no physical card to remove or steal, reducing the risk of SIM theft and fraud.

Winner: eSIM

2. Protection Against SIM Swapping Attacks

SIM swapping fraud happens when hackers trick your mobile provider into transferring your phone number to a new SIM card that they control. This allows them to access your accounts by resetting passwords linked to your phone number.

eSIMs make SIM swapping harder because they require digital authentication before being transferred to another device. Many carriers require stronger identity verification before allowing an eSIM transfer, such as:

• Biometric authentication (Face ID or fingerprint)
• Carrier login and security codes
• Multi-factor authentication (MFA)

This makes it more difficult for criminals to convince a mobile carrier to switch your number to another device.

Winner: eSIM

3. Privacy From Physical Tracking

Traditional SIM cards can be tracked when inserted into a device, making it easier for someone to monitor a specific SIM card’s location.

With an eSIM, users can switch profiles or carriers digitally without needing a new physical card. If needed, an eSIM user can disable or remove an eSIM profile remotely, making tracking more difficult.

This feature is especially useful for journalists, activists, and individuals in high-risk areas who may want to reduce the risk of being tracked by removing their mobile connection without physically handling a SIM card.

Winner: eSIM

4. Easier Remote Disabling and Deletion

If your phone is lost or stolen, a traditional SIM card can still be used unless you contact your carrier to deactivate it. If someone removes your SIM card before you can report it lost, they may still be able to use it.

eSIMs, however, can be deactivated remotely by logging into your carrier’s account. If your phone is stolen, you can erase your eSIM profile and prevent it from being used.

Additionally, some devices, like iPhones, allow users to remotely wipe the entire phone, including eSIM data, making it completely useless to thieves.

Winner: eSIM

5. Anonymity and Multiple Profiles

eSIMs allow users to store multiple profiles (different phone numbers or carriers) on the same device. This means you can:

• Use a temporary phone number for certain activities and delete it when no longer needed.
• Switch between personal and work numbers without carrying two SIM cards or phones.
• Easily change carriers without going to a store or buying a physical SIM.

With a traditional SIM card, you would need a new physical SIM each time you switch numbers or carriers, making it less flexible and harder to stay anonymous.

Winner: eSIM

6. Carrier Control and Privacy Risks

One downside of eSIMs is that you have less control over switching devices compared to a traditional SIM. Since eSIMs are digitally activated by carriers, some providers may lock an eSIM to a specific phone, making it harder to switch phones freely.

Additionally, in some cases, mobile providers might still collect location and usage data from eSIMs, just like they do with traditional SIM cards.

Winner: Traditional SIM (for full control over switching devices)

7. Which One is Better for Privacy?

Final Thoughts

A SIM card is an essential component of your mobile phone, storing critical information that allows you to access your carrier’s network securely. While it does not store personal files or multimedia, it holds unique identification details, network authentication keys, and limited contact and message storage.

With advancements like eSIM technology, the traditional SIM card may eventually disappear, but for now, it remains a vital part of mobile communication. If you ever lose your SIM card, contact your mobile provider immediately to prevent unauthorized use. Understanding the role and limitations of your SIM card can help you make informed decisions about your mobile experience and prepare for the future of connectivity.