What is a SIM card? Get all your questions answered 

Phones are important. We use them for calling, messaging, browsing, streaming. And we’d be lost without our phone cameras to capture unexpected special moments. But have you ever stopped to think that it’s actually the SIM card inside that makes all the good stuff possible? 

We’ve all heard of SIM cards, but do you know what a SIM card is? That tiny chip is a total game-changer, so this article will tell you everything you need to know about what SIM cards are. Ready to get the most out of your phone?

A SIM card is a small plastic card with a computer chip that slots into your phone.  
 
SIM cards come in three sizes: standard, micro and nano. SIM cards are used in smartphones all over the world, but the exact SIM card you need depends on your phone.

SIM stands for Subscriber Identity Module. 

SIMs are computer chips that hold information and allow you to connect with your network. This means you can make calls, send SMS messages and connect to mobile internet services like 3G, 4G, and 5G.

They’re also transferable, and you can choose to save messages, contacts and emails to them. So, have you ever wondered what happens if you put your SIM card into another phone? If you change devices or have an accident with your phone and need to borrow a friend’s, it’s no hassle. If the other phone uses the same size of SIM, just pop your SIM card into the new handset and you’re good to go. 

SIMs have an ID number or IMSI, which stands for International Mobile Subscriber Identity. This number identifies the phone to the network. Along with your IMSI, your SIM will also have a unique MSISDN. This is short for Mobile Subscriber Integrated Services Digital Network Number. 

Yes, it does. When you purchase a SIM card, it will typically come pre-assigned with a phone number by the mobile network operator. This phone number is tied to the SIM card itself, allowing you to make calls, send texts, and access mobile data services when inserted into a compatible device.  
 
If you purchase a new phone with a bundled SIM card, the phone number will be assigned to the SIM provided as part of the package.

In addition to their key role in SIM identification, SIM cards can also store contact information, telephone numbers, SMS messages, billing information, and data usage. Plus, your SIM will have its own personal identification number (PIN) to protect against theft.

Yes, an increasing number of users are now taking advantage of eSIM. These allow you to transfer network connectivity and data (such as contacts, apps and photos) between your old device and your new one without the need for a physical SIM card.  
 
Find out more on our eSIM page.

Your SIM card cost will depend very much on the package of text, calls and data you select. Take a look at our great range of SIM Only deals from only £11 a month to find your ideal option

It’s easy to save your contacts onto your SIM card as well as your phone, if you have enough space on your card and your phone has this option. 
 
First go to your address book by choosing Menu then Contacts. 
 
Pick Options and Settings. 
 
Now select Copy to phone/SIM, then Save contacts to SIM. 
 
It’ll usually take a few minutes to complete. Some phones may ask you to select contacts if they can’t move them all at once.  
 
We’ve got a great range of SIMs available and they’re all 5G Ready, at no extra cost. We’ve also recently launched our brand new Supercharged Pay As You Go Data Packs. Get yours today.