Just about every cellular phone in existence today makes utilize of a SIM card. "SIM" is short for Subscriber Identity Module. Without it, you tin can't make or receive phone calls. You besides can't use any internet information over a cellular connection.

You probably already knew this, but why is your telephone and so useless without this small piece of metal and plastic? Just what is a SIM carte du jour actually used for?

What a SIM Carte Looks Like

A SIM Card is pretty like shooting fish in a barrel to place. It's a plastic carte with a distinct gear up of metal contacts. Inside the SIM card you'll notice an integrated excursion, which communicates with the telephone through the aforementioned metal contacts.

SIM cards come in a variety of shapes and sizes. In fact, there are four sizes in total. The largest is known as "full-size" and is effectively obsolete. Measuring 3.37 in past 2.125 in, full-size SIM cards were basically the size of smart access cards.

The reason for this is quite interesting. At the outset of mobile phone engineering science, multiple people would share a single telephone. The idea was that you would insert your enormous SIM card into the phone when you wanted to utilise it. Since the carte would spend more time in your wallet than in a phone, the big plastic body fabricated perfect sense.

These days nigh SIM cards y'all'll buy have all three of the mutual sizes, with pieces of the plastic body breaking away until you lot reach the size yous want. The Mini-SIM size is pretty uncommon these days and is generally used in legacy devices or depression-toll devices based on older designs.

The Micro-SIM size is very pop and most mainstream phones use this. The Nano-SIM size eliminates virtually all plastic body around the SIM contacts and is essentially the standard for flagship and mid-high-finish smartphones, where internal space is at an extreme premium. SIM cards are physically keyed to go far impossible to insert them the wrong way around.

Here's a tip: don't throw away the Mini- and Micro-SIM frames when you become a new SIM carte du jour. If you always demand to motility the SIM to another phone yous may nevertheless need them!

What Does a SIM Bill of fare Do?

The cellular network owned by your service provider is just that –  a network. They need to control who has access to that network both for security reasons and to brand the whole affair work!

Then what is a SIM card? Your SIM carte is an access card. Information technology contains your credentials. Then in that sense it's similar a card that stores your username and countersign. You "log in" to the cellular network with the SIM carte du jour. Your telephone number is your unique network identity.

No affair where you become, every bit long as you are within range of a cellular tower belonging to your service provider, you tin can exist reached and reach others.

What's Stored On a SIM?

The SIM carte du jour has information on information technology that the network needs to authenticate your business relationship. 1 of these is the ICCID or Integrated Circuit Card Identifier. This is a number that'due south unique to that 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. They fundamental is run through a cryptographic function then compared to another adding washed with a copy of the cardinal stored in the carrier'southward database. If they match, you're let onto the network.

The SIM also has memory on it, that you lot tin use to store your contacts and text messages. This is pretty limited however, with well-nigh SIMs sporting between 64k and 256k of infinite. These days about people are better off storing their contacts on the telephone's own memory, along with a backup using something like iCloud or their Google account.

Contract and Prepaid SIM Cards

At that place are by and large two models cellular providers utilize to sell their services to customers. You tin can sign a fixed contract agreement, or you can exist a prepaid client.

In both cases, you'll become a SIM card. The cards themselves are no different from each other. Rather, information technology's how the provider handles the business relationship that sets them apart. You tin can buy prepaid SIM cards off the shelf. Although in many countries you must register the purchase, using regime ID and proof of residence.

Contract SIM cards are allocated data, talk time and other resource according to your contract. Overages are added to your bill and at the end of the billing bike the money gets deducted from your account. With prepaid cards, you'll unremarkably load a monetary amount onto the SIM or otherwise purchase talk time or mobile information upfront.

Depending on where you live, certain contract handsets may be locked to SIM cards but from that provider. Often this is a mode to get a phone for a substantial disbelieve, but if y'all e'er need to utilise another SIM menu, peradventure when travelling, y'all'll notice that information technology doesn't work! To avoid that sort of situation, be sure to look for phones sold as "unlocked".

Switching SIM Cards

Taking a SIM from one phone and moving it to another is pretty painless. Given that both phones use the same SIM card size. If the other telephone uses a larger size, yous'll take to use an adapter to make information technology fit the larger slot. If the SIM card you lot desire to employ is also large for the target phone, y'all accept ii choices.

The first is to cut the SIM down to size. Some people are brave enough to do this using zip merely a pair of pair of scissors and some sort of template. If y'all accidentally cut into the circuity of the SIM carte, it's game over and you'll need a new one. The safest mode to do this is past using a dedicated SIM cutting tool. Even and then, you run the hazard of destroying the card, so have this route just at your own risk.

The other option is to switch SIM cards.  Of course, if you lot just went out and bought a new SIM card, it would take a dissimilar telephone number associated with it! Each service provider may have a unlike procedure to move your phone number from 1 SIM to some other.

In general however, it should simply take a phone call and verification of your identity. If the provider has physical stores, you lot should fifty-fifty have the option of going in for a new SIM, with your old ane disabled.

These days information technology's popular to utilize text letters sent to specific SIM cards equally a class of 2-gene authentication. And so at present we have something known as SIM-swap fraud. Where criminals notice ways to have your phone number transferred to a SIM they control. SIM duplication is another method. Information technology's certainly something to watch out for.

Life Afterwards SIM Cards

SIM cards, at least discrete SIM cards, aren't really necessary anymore. We are already seeing the rise of the eSIM or embedded SIM card. This is a SIM card built directly into the phone. This card is programmable, which means you tin can easily change providers or utilise multiple providers at once.

In some countries, "dual-SIM" phones have been very popular. With these you lot could have two telephone numbers, one for personal apply, for example. You could besides have a dedicated data SIM bill of fare, maybe with better rates.

eSIMs make this redundant and turns access and authentication into something like to fixed-line broadband usage. Where you just enter a username and countersign to access a given service provider.

Few current phones have embedded SIM cards at the time of writing, merely that'southward set to change as the manufacture adopts this new standard. Y'all next phone might very well accept no identify to put a SIM carte du jour at all, which would be the end of an era, but certainly a movement for the better.