A SIM card stores the details your carrier needs to recognize you on its network: your subscriber identity (IMSI), a secret authentication key, the SIM's own serial number (ICCID), your PIN and PUK codes, and some carrier settings. It can also hold a small number of contacts and text messages, mostly on older phones. It does not store your photos, videos, apps or chats. Those live on your phone or in the cloud. Here's what's on the chip, what isn't, how to check it, and what the numbers printed on your SIM card mean.
What information is stored on a SIM card?
SIM stands for Subscriber Identity Module. It's a small chip that proves to your carrier that you're a paying customer, so you can make calls, send texts and use mobile data. For a full intro, see what a SIM card is and what it does. Here's what the chip actually holds.
Your subscriber identity (IMSI)
The International Mobile Subscriber Identity is the number your carrier uses to identify your subscription on its network. It has up to 15 digits and is made of three parts (3GPP TS 23.003, ITU-T E.212):
- Mobile Country Code (MCC): 3 digits for the country of your carrier.
- Mobile Network Code (MNC): 2 or 3 digits for the carrier itself.
- Mobile Subscriber Identification Number (MSIN): the rest, which identifies you within that carrier.
The IMSI is not your phone number. More detail in our guide to the IMSI number.
A secret authentication key (Ki)
Each SIM holds a secret 128-bit key that only the SIM and your carrier know (3GPP TS 33.102). When you connect, the network sends a challenge and the SIM answers it using this key. That's how the network knows your SIM is genuine. The key is never sent over the air.
The SIM serial number (ICCID)
The Integrated Circuit Card Identifier is the unique serial number of the card itself. It's usually printed on the SIM and stored on the chip. See below for what its digits mean, or read our full guide to the ICCID number.
Your PIN and PUK codes
The SIM PIN locks your SIM, so nobody can use it in another phone without the code. Under the SIM card standard, the PIN gets blocked after 3 wrong tries in a row. You then need the PUK (PIN Unblocking Key) from your carrier. After 10 wrong PUK tries, the PUK itself is blocked for good (ETSI TS 102 221). Apple's advice: never guess your SIM PIN or PUK, because a wrong guess can permanently lock your SIM card or eSIM (Apple: Use a SIM PIN for your iPhone or iPad). Lost yours? See what a PUK code is and where to find it.
Carrier and network data
The SIM also carries settings your carrier puts there (3GPP TS 31.102):
- Service Provider Name (SPN): the carrier name your phone shows in the status bar.
- SMS center number (SMSC): the address of the center that sends and delivers your text messages.
- Service numbers (SDN): short numbers for things like voicemail or your balance.
- Preferred networks: lists that help your phone pick a partner network when you roam abroad.
- Last location area (LAI): the area code of the network cell your SIM last registered in, made of the MCC, the MNC and a location area code.
- Call cost counters (Advice of Charge): an older feature some carriers use to show the cost of calls.
- Your phone number (MSISDN): there's a field for it, but it's optional and carriers don't always fill it in. That's why some phones can't show your own number.
Contacts and text messages (mostly older phones)
A SIM card has a small phonebook and room for some text messages. Older phones saved contacts and SMS there by default, so you could move them to a new phone with the SIM. Modern phones save contacts to your phone or to an account like iCloud or Google instead. An iPhone doesn't store contacts on the SIM card at all, but it can import them from an old SIM (Apple: Import contacts from your SIM card to your iPhone).
What a SIM card does not store
SIM storage is tiny compared with your phone's storage. So most of what's on your phone has nothing to do with the SIM:
- Photos and videos: saved on your phone's storage, a memory card or a cloud backup.
- Apps and app data: installed on the phone, not the SIM.
- WhatsApp, iMessage and other chats: stored on the phone and in the app's own backup.
- Passwords, emails and browsing history: on the phone or in your accounts.
- Contacts saved by a modern phone: usually on the phone or synced to iCloud or Google.
- Your name and ID details: if your SIM was registered to you, those details are kept by your carrier, not on the chip.
So if you swap SIM cards, your photos and apps stay where they are. And if you lose your SIM, nobody gets your photos from it.
How to see what's on your SIM card
You can't open a SIM like a folder, but you can see its main details on your phone.
On iPhone
- ICCID and EID: go to Settings > General > About and scroll down (Apple: Find the serial number or IMEI on your iPhone).
- Contacts on an old SIM: insert it, then go to Settings > Apps > Contacts > Import SIM Contacts.
- SIM PIN: go to Settings > Cellular > SIM PIN (on dual SIM, pick the line first).
On Android
- SIM status: open Settings > About phone and look for your SIM status or phone number. Menu names vary by brand.
- Contacts on the SIM: in the Contacts app, look for an option like Manage SIM or Import from SIM (EE: Import contacts from your SIM on a Pixel 9).
Dialing *#06# shows your phone's IMEI (and EID if it supports eSIM). Those numbers belong to the phone, not the SIM.
Can you check who a SIM is registered to?
Not from the SIM itself. The owner's name and ID are kept by the carrier. In some countries you can check which SIMs are registered in your own name. In Pakistan, for example, the PTA's SIM Information System shows how many SIMs are registered to your CNIC (cnic.sims.pk). Be careful with unofficial "SIM data" websites that claim to show someone else's details.
The numbers on a SIM card, explained
Wondering how many digits a SIM card number has? It depends on which number you look at:
- ICCID (printed on the card): the current ITU standard sets it at 19 digits (ITU-T E.118). The SIM stores it in a field with room for 20 digits, so some cards show 20. It starts with 89 (the code for telecoms), then a country code, then the issuer and the card's own number. The last digit is a check digit.
- IMSI (stored on the chip): up to 15 digits. It's usually not printed on the card.
- PIN: a short code you type when the phone starts. Your carrier gives you a default one, often 4 digits, which you can change.
- PUK: usually 8 digits, printed on the card holder your SIM came in or available from your carrier.
- Your phone number: not part of the ICCID. You'll usually find it on the SIM's packaging or in your carrier account.
SIM card sizes and eSIM
Four sizes, the same chip
Physical SIM cards come in four formats (ETSI TS 102 221):
- Full-size: credit card size, now just the card the SIM comes in.
- Mini SIM (standard): 25 x 15 mm.
- Micro SIM: 15 x 12 mm.
- Nano SIM: 12.3 x 8.8 mm, the smallest size and the one recent phones with a SIM tray usually take.
The chip and its data are the same. Only the plastic around it changes. More in our guide to the types of SIM cards.
What about eSIM?
An eSIM is a SIM chip built into your phone. Instead of a plastic card, your carrier sends a digital profile that you download. That profile holds the same kind of information as a SIM card, like the IMSI, the authentication key and an ICCID. The chip also has its own ID, the EID. Some phones don't take a physical SIM at all: the iPhone Air, for example, only works with eSIM (Apple: iPhone Air tech specs).
Want to know more? Read what an eSIM is, compare SIM cards vs eSIM, or see how to convert a physical SIM to an eSIM.
eSIM is handy when you travel. Many eSIM phones let you add a travel eSIM for data while your usual SIM stays in place, so your number keeps working for texts and calls. If you have a trip coming up and your phone supports eSIM, you can pick a data plan for your destination before you go.
Europe, USA and Asia plans shown · data-only eSIMs, no phone number · Find the eSIM for your destination
FAQs
What does SIM stand for?
Subscriber Identity Module. It's the chip that identifies you to your mobile carrier.
What information is stored on a SIM card?
Your IMSI (subscriber identity), a secret authentication key, the ICCID serial number, your PIN and PUK, and carrier settings like the network name and SMS center number. It can also hold some contacts and text messages.
Does a SIM card store photos or apps?
No. Photos, videos, apps and chats are stored on your phone, a memory card or in the cloud. The SIM has very little space.
Does my SIM card store my contacts?
Only if they were saved to the SIM, which mostly happened on older phones. Modern phones save contacts to the phone or to iCloud or Google. You can import contacts from an old SIM on iPhone and Android.
How many digits does a SIM card number have?
The ICCID printed on the card has 19 digits under the current ITU standard, and some cards show 20. It starts with 89. The IMSI has up to 15 digits, the PIN is often 4 digits, and the PUK is usually 8.
What happens if I put my SIM card in another phone?
Your number and plan move with it, as long as the new phone is unlocked or locked to the same carrier. Your photos, apps and most contacts stay on the old phone. See how to put a SIM card in a different phone.
Can someone get my personal information from my SIM card?
Not much. The SIM doesn't hold your photos, messages from apps or ID details. With your SIM, someone could use your number, so turn on a SIM PIN to protect it.
Does an eSIM store the same information as a SIM card?
Yes, the same kind. An eSIM profile has an IMSI, an authentication key and an ICCID, just like a physical SIM. It's downloaded to a chip built into your phone instead of sitting on a plastic card.