Why is that tiny chip in your phone so important? All the questions you've ever had about your SIM card, finally answered.

Phones are important. We use them for chatting or messaging our friends, listening to music and for Googling weird and wonderful facts. We’d be lost without our phone cameras to capture unexpected special moments. But, ever stopped to think that it’s actually the SIM inside that makes all the good stuff possible?

That tiny chip is a total game-changer. Plus, knowing all the tricks of the trade can help you get the most out of your phone. Here are the most frequently asked SIM-related questions, and their answers.

1. What is a SIM card?

SIM stands for subscriber identity module and it’s a small plastic card that slots into your phone. Good to know for all those online quizzes. It’s also used in smartphones all over the world.

2. What does a SIM do?

SIMs are computer chips which 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, if you had an accident with your phone and you needed to borrow someone else’s urgently, it’s no hassle. Just pop in the SIM card and you can call one of your contacts or use your data. Just make sure they use the same size of SIM first.

3. What is stored on a SIM card?

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. Despite the complicated name, it’s basically your phone number.
They can also store contact information, telephone numbers, SMS messages, billing information and data usage. Plus, your SIM will have a personal identification number (PIN) to protect against theft.

4. How to activate your SIM card

Activating a SIM card is simple as long as your SIM is valid, unlocked and provided by your network. Check out our SIM Support page and choose your reason so we can give you the best advice.

5. How to remove the SIM card from your iPhone

To remove the SIM, first you’ll need to find the SIM tray. For most models, this will be on the right-hand side. But for the Original iPhone, iPhone 3GS or iPhone 3G, it’ll be on the top.

Once you’ve found it, insert something like a paper clip into the hole beside the tray and push in gently. The tray should release easily, and you can insert the new SIM. If you’ve got any problems, take your device to your local phone or Apple shop. They’ll be happy to help.

6. Inserting the SIM card into your iPhone

Once you’ve taken out your old SIM with our guide above, you’re ready to put your new one in.
Identify where the notch is and place your SIM on the tray, so that it fits perfectly. Then push the tray back into the device.

7. How to remove the SIM card from your Samsung

First, check if your Samsung phone has a removable back cover. Phones from 2014 or earlier will, but if you have a newer phone it should have a sealed battery.

Removable back cover devices

Remove the back cover and then take the battery out.
Carefully slide the SIM out of the SIM slot.

Sealed battery devices

If the battery is sealed, then you’ll need to find your SIM tray. Your product manual will also show you where this is.
Insert the ejection pin into the hole on the SIM tray.
Gently pull the SIM tray open and remove the SIM card.

8. Inserting the SIM card into your Samsung

See our guide for removing your old SIM above, then place your new SIM in the tray. Make sure the gold contacts are facing downwards. Then slide the SIM slowly back in.

9. How much is a SIM card

Take a look at our great range of SIM deals from only £11 a month.

10. How to save contacts to your SIM card

It’s easy to save your contacts 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’ or any similar choices like ‘Move 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. If you do choose to ‘copy’ instead of ‘move’, you’ll also see each contact showing twice. This is because one list is stored on your SIM and one on your phone.

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 Pay As You Go Supercharged Data Packs. Get yours today.