Almost every cell phone in existence today uses a SIM card. “SIM” is short for Subscriber Identity Module. Without it, you won’t be able to make and receive phone calls. You also cannot use internet data over a cellular network.
You probably already knew this, but why is your phone so useless without this little piece of metal and plastic? What is a SIM card actually used for?
What does a SIM card look like
The SIM card is fairly easy to identify. This is a plastic card with a clear set of metal contacts. Inside the SIM card, you will find an integrated circuit that communicates with the phone through the aforementioned metal contacts.
SIM cards come in different shapes and sizes. There are actually four sizes in total. The largest of these is known as “full size” and is virtually obsolete. Full-size SIM cards measuring 3.37 inches by 2.125 inches were mostly the size of smart access cards.
The reason for this is quite interesting. In the early days of mobile phone technology, several people used the same phone. The idea was that you could insert your huge SIM card into your phone whenever you want to use it. Since the card will spend more time in your wallet than in your phone, a large plastic case makes sense.
Most of the SIMs you buy these days come in all three regular sizes, and parts of the plastic case break off until you reach the size you want. Mini SIM size is quite unusual these days and is mostly used in legacy devices or low-cost devices based on older designs.
Micro-SIM size is very popular and most regular phones use it. The size of the Nano-SIM eliminates almost all of the plastic casing around the SIM contacts and is essentially the standard for flagship and mid-range smartphones where interior space is extremely expensive. SIM cards have a physical key so that they cannot be inserted incorrectly.
Tip: Don’t throw away the Mini and Micro SIM frames when you get a new SIM card. If you ever need to swap your SIM card to another phone, you might still need them!
What does a SIM card do?
The cellular network owned by your carrier is the network. They need to control who has access to this network, both for security reasons and in order for it to work!
So what is a SIM card? Your SIM card is an access card. It contains your credentials. In that sense, it is like a card that stores your username and password. You “log in” to the cellular network using your SIM card. Your phone number is your unique online identifier.
No matter where you go, as long as you are within reach of your carrier’s cell tower, you can be contacted and contacted by others.
What is stored on the SIM card?
The SIM contains the information the network needs to authenticate your account. One of these is ICCID or Integrated Circuit Card ID . This is a unique number for a specific physical SIM card.
The next important bit of data on the SIM is known as the Authentication Key . This is a cryptographic key used to sign data sent to the cellular network. Their key is passed through a cryptographic function and then compared with another calculation performed against a copy of the key stored in the operator’s database. If they match, you are allowed on the network.
The SIM also has memory that you can use to store contacts and text messages. This is rather limited, however, as most SIMs are between 64KB and 256KB. Most people these days are better off storing their contacts in their own phone memory along with a backup using something like iCloud or their Google account
Contractual and Prepaid SIM Cards
There are usually two models that cellular operators use to sell their services to customers. You can sign a fixed contract or be a prepaid customer.
In both cases, you will receive a SIM card. The cards themselves are no different from each other. Rather, what sets them apart is how the vendor handles the account. You can buy ready-made prepaid SIM cards. Although in many countries, you must register your purchase using a government ID and proof of residence.
Contract SIMs are allocated data, talk time and other resources in accordance with your contract. The surplus is added to your account and money is debited from your account at the end of the billing cycle. When using prepaid cards, you usually load an amount of money onto the SIM card or pay in advance for call time or mobile internet.
Depending on where you live, some contract phones may only be linked to this provider’s SIM cards. This is often a way to get a phone at a significant discount, but if you ever need to use a different SIM card while traveling, for example, you will find that it doesn’t work! To avoid this situation, be sure to look for phones sold as “unlocked“.
Switch SIM Cards
Removing the SIM from one phone and moving it to another is pretty painless Considering both phones use the same size SIM. If the other phone is larger, you will need an adapter to fit the larger connector. If the SIM you want to use is too large for the target phone, you have two options.
The first is to trim the SIM card to the correct size. Some people are brave enough to do this using only scissors and some kind of template. If you accidentally interrupt the SIM circuit, the game is over and you will need a new one. The safest way to do this is to use a dedicated SIM card cutting tool. Even so, you run the risk of ruining the map, so choose this route only at your own peril and risk.
Another option is to change your SIM card. Of course, if you just went out and bought a new SIM, a different phone number would be associated with it! Each service provider may have their own procedure for transferring a phone number from one SIM card to another.
In general, however, he should just take the phone call and verify your identity. If the provider has physical stores, you should even be able to purchase a new SIM by unplugging the old one.
It is popular these days to use text messages sent to specific SIM cards as a form of two-factor authentication. So now we have something known as a SIM swap scam. Where criminals find ways to transfer your phone number to the SIM card they control. Duplicating a SIM card is another method. This is definitely something to look out for.
Life After SIM Cards
SIM cards, at least discrete SIM cards, are no longer needed. We are already seeing the rise in popularity of eSIM or embedded SIM cards. It’s a SIM card built right into your phone. This card is programmable, which means you can easily change providers or use multiple providers at once.
Dual SIM phones are very popular in some countries. With their help, you can have two phone numbers, one, for example, for personal use. You might also have a dedicated data SIM, possibly with higher rates.
eSIMs make this redundant and turn access and authentication into something akin to using fixed broadband. Here, you simply enter your username and password to access a specific service provider.
At the time of this writing, not many modern phones have built-in SIM cards, but that will change as the industry embraces this new standard. The next phone may well run out of space for a SIM card, which will be the end of an era, but definitely a step for the better.