Everything you ever wanted to know about your SIM card.
What Is a SIM card?
Modern-day mobile phones come in two main varieties, namely Code Division Multiple Access (CDMA) and Global System for Mobile (GSM). While CDMA phones don’t require a SIM card, GSM models do, and they happen to be the more popular of the two options.
Basically, a SIM card is a tiny card that’s placed on the back of a GSM smartphone. A SIM card is the critical component in your phone that allows you to connect to a carrier network to make calls, send text messages, surf the internet and more.
Back in the good old days, telephone had physical wires linking one end to another. Whenever you have dialed a number your phone company could row your call exactly where it needed to using said cables but in this brave new world of not only phone calls but vibes, Facebook and snapchats and other stuffs that kids are doing being blasted out from cell towers everywhere. These signals have to know where they are going every time. This is where SIM cards come in and SIM stands for "Subscriber Identity Module" which gives a pretty big hint of what it does. It identifies what the mobile phone subscriber is using, maybe it is a particular iPhone, Galaxy or a Window phone.
SIM cards store a 64-bit number that serves as a unique identifier and although that only takes up to 8 Bytes of storage, there are over 9 quintillion unique numbers that can be stored in this way on a SIM card. So this method should work no matter how many people sign up for a single operator.
How does a SIM card work?
When you turn on your phone and first connect to the cell network, your phone will pass your SIM cards ID number along with an authentication key also found on the SIM card to your cell phone provider. Your provider then generates a random number and uses the key to spit out a response number at the same time, that random number is sent back to your and the same calculation is done with the authentication key to generate another response number, if the two numbers match then your service provider will recognize this and connect your phone to the network both ensuring that it's actually you that's connected to keep your data safe and to see who you are.
All messages from your phone to the network are in a secret code. The key to encrypt and decrypt messages is stored in the SIM card. This provides communication privacy. The SIM card chip also stores specific data such as the name of your service provider, your card’s unique serial number, your PUK code, last dialed numbers and your PIN code. Your SIM card is also where the International Mobile Subscriber Identity (IMSI) and its authentication key are kept. This key is provided by your carrier and it connects your phone number with your device. This means that when someone dials your number, the call will go the exact phone that you have.
SIM cards are the unseen magicians of today's smartphones. They make connecting to networks and switching phones as easy as removing a small metal tray.
If you buy a new phone, you can simply insert your existing SIM and keep on using your existing service as long as the new phone isn't locked to a different carrier. Likewise, if you travel internationally you can just buy a SIM card from a local carrier — as long as your phone isn't locked to a carrier.
Other than just identifying information. SIM cards can also store phonebook information and although that might seem like a dated concept in an age where phones can store almost anything you can think of on separate internal memory or expansion cards. This was important when things like flip phones were more popular so you wouldn't lose all your contact info when you upgrade it or if you're not storing your phonebook with a Google or Apple cloud service.
Sim cards are quite useful when you want to switch phones. Although, SIM cards are quite low capacity with many of them holding well under a megabyte of data, the small amount of information that they do hold is extremely important also if you want your phone to be of any use when you don't have a Wi-Fi signal, the SIM card is very important here.
If you are moving cards between phones just make sure that they are the same size as there different sim form factors. There are a variety of SIM cards that could be used on carrier networks, including the Full SIM, Mini SIM, Micro SIM and Nano SIM. Today, there are two more types of SIM cards without any size at all: an embedded SIM, or eSIM. These new SIM cards are entirely virtual.
SIM card sizes differences matter greatly to device makers. The smaller the SIM, the less room it takes up in increasingly thin smartphones.
We should also note that a Mini SIM can be converted into a Micro SIM by cutting the plastic in the larger Mini SIM. You’ll find some carriers do that when you upgrade an older phone.
What is Dual SIM and why does it matter?
Dual SIM technology is typically only found in higher-end devices, but it’s an important feature that brings significant value to smartphone users.
With Dual SIM, you can insert two SIM cards into your device at the same time, allowing you to have two numbers on one network or two numbers on different networks. It’s especially handy for business users who want to have one line for personal use and another for business use. Dual SIM can also come in handy for world travelers who might use one network connection for domestic use and another for international travel.
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.
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