Just nearly every cellular telephone in existence today makes use of a SIM card. "SIM" is short for Subscriber Identity Module. Without it, y'all can't brand or receive phone calls. You besides can't use any cyberspace data over a cellular connexion.

You probably already knew this, only why is your phone so useless without this small piece of metallic and plastic? Just what is a SIM menu really used for?

What a SIM Carte du jour Looks Like

A SIM Card is pretty easy to identify. Information technology's a plastic card with a singled-out set of metal contacts. Inside the SIM carte du jour y'all'll detect an integrated circuit, which communicates with the telephone through the aforementioned metallic contacts.

SIM cards come in a diverseness of shapes and sizes. In fact, there are iv sizes in total. The largest is known equally "total-size" and is effectively obsolete. Measuring iii.37 in by 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 technology, multiple people would share a unmarried phone. The idea was that you would insert your enormous SIM carte du jour into the phone when yous wanted to apply it. Since the bill of fare would spend more time in your wallet than in a telephone, the big plastic body fabricated perfect sense.

These days most SIM cards you'll buy have all three of the common sizes, with pieces of the plastic torso breaking abroad until you lot attain the size you lot want. The Mini-SIM size is pretty uncommon these days and is by and large used in legacy devices or low-price devices based on older designs.

The Micro-SIM size is very popular and most mainstream phones use this. The Nano-SIM size eliminates well-nigh all plastic body around the SIM contacts and is essentially the standard for flagship and mid-high-end smartphones, where internal space is at an extreme premium. SIM cards are physically keyed to make information technology impossible to insert them the incorrect manner 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 ever need to movement the SIM to another phone you may still demand them!

What Does a SIM Card Do?

The cellular network owned past your service provider is simply that –  a network. They need to control who has admission to that network both for security reasons and to make the whole thing work!

And then what is a SIM card? Your SIM card is an admission card. Information technology contains your credentials. Then in that sense it's like a bill of fare that stores your username and countersign. You "log in" to the cellular network with the SIM card. Your telephone number is your unique network identity.

No matter where you get, as long as you are within range of a cellular tower belonging to your service provider, you tin can be reached and attain others.

What'southward Stored On a SIM?

The SIM card has information on it that the network needs to cosign your account. I of these is the ICCID or Integrated Circuit Card Identifier. This is a number that's unique to that specific physical SIM carte.

The next important bit of information on the SIM is known as the authentication key. This is a cryptographic key used to sign information sent to the cellular network. They key is run through a cryptographic part and then compared to some other calculation done with a re-create of the key stored in the carrier'southward database. If they match, you're let onto the network.

The SIM likewise has memory on information technology, that you can utilize to store your contacts and text letters. This is pretty express however, with almost SIMs sporting between 64k and 256k of space. These days most people are better off storing their contacts on the phone'southward ain retentivity, forth with a backup using something like iCloud or their Google business relationship.

Contract and Prepaid SIM Cards

There are generally two models cellular providers use to sell their services to customers. You tin sign a fixed contract agreement, or y'all tin can be a prepaid client.

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

Contract SIM cards are allocated data, talk fourth dimension and other resources according to your contract. Overages are added to your beak and at the finish of the billing bike the money gets deducted from your business relationship. With prepaid cards, you'll unremarkably load a monetary amount onto the SIM or otherwise purchase talk time or mobile data upfront.

Depending on where you live, certain contract handsets may be locked to SIM cards only from that provider. Ofttimes this is a way to get a phone for a substantial discount, merely if y'all always need to use another SIM bill of fare, perhaps when travelling, yous'll find that it doesn't work! To avert that sort of situation, be certain to look for phones sold as "unlocked".

Switching SIM Cards

Taking a SIM from one phone and moving information technology to another is pretty painless. Given that both phones use the same SIM card size. If the other phone uses a larger size, you'll have to use an adapter to arrive fit the larger slot. If the SIM carte du jour you want to use is too large for the target phone, y'all have two choices.

The get-go is to cut the SIM down to size. Some people are dauntless enough to practice this using nothing but a pair of scissors and some sort of template. If you accidentally cut into the circuity of the SIM menu, it'southward game over and you'll demand a new one. The safest way to do this is past using a dedicated SIM cutting tool. Even then, you run the risk of destroying the carte, so take this route just at your own risk.

The other option is to switch SIM cards.  Of course, if you but went out and bought a new SIM card, it would have a different phone number associated with it! Each service provider may have a unlike procedure to movement your phone number from ane SIM to another.

In general however, it should but take a telephone telephone call and verification of your identity. If the provider has physical stores, y'all should even have the option of going in for a new SIM, with your old one disabled.

These days information technology's popular to use text letters sent to specific SIM cards as a form of two-factor hallmark. So now nosotros have something known as SIM-swap fraud. Where criminals find ways to have your telephone number transferred to a SIM they control. SIM duplication is another method. It's certainly something to watch out for.

Life After SIM Cards

SIM cards, at least detached 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 direct into the telephone. This menu is programmable, which means you tin can easily change providers or employ multiple providers at one time.

In some countries, "dual-SIM" phones have been very popular. With these you lot could take two telephone numbers, 1 for personal use, for instance. Yous could also have a dedicated data SIM card, perhaps with meliorate rates.

eSIMs brand this redundant and turns access and authentication into something similar to fixed-line broadband usage. Where you simply 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's set to change as the manufacture adopts this new standard. You next telephone might very well have no place to put a SIM bill of fare at all, which would be the finish of an era, simply certainly a move for the better.