This website uses cookies to ensure you get the best experience on our website. OK
536 Shares 11 comments

What's a SIM card and why do I need one?

There are now Mini, Micro and Nano SIMs in frequent use, but why? Do we need any of them? They can be a blessing and a curse, depending on your situation. Here's where SIMs came from, why they still exist, and an answer to whether we will continue to need the things at all.

huawei p8 dual sim
We all know them well, but do we love them? Do we need them? / © ANDROIDPIT

What is a SIM card?

SIM stands for Subscriber Identity Module. The card itself is a way of tying a customer to a carrier. It is used to identify and authenticate any subscriber and grant them access to a mobile network.

On the card is stored what's called an International Mobile Subscriber Identity (IMSI) and an authentication key, which pairs with the IMSI. 

The IMSI is sent out by the phone and used by the network to identify the subscriber. An algorithm is then used by the SIM to send another number to the network, which the network compares with its own computation. If the numbers match, the subscriber is deemed legitimate and granted network access.

AndroidPIT roaming travelling 1
GSM and, therefore, SIM cards were European inventions. / © ANDROIDPIT

SIM cards are only strictly necessary on GSM networks, which were developed in Europe by the European Telecommunications Standards Institute, to its benefit. The large amount of cross-border travel that occurs in Europe necessitates frequent switching of carriers, something that SIM cards allow.

In the US, crossing borders is not such a significant problem due to the size of the country, and some carriers opted for CDMA networks, which don't require SIM cards. Verizon, until only relatively recently, did not require their subscribers to have SIM cards, but now that they are increasingly utilizing LTE network coverage, which is based on GSM technology, most of their phones have migrated to SIM cards.

The problem with SIMs

SIM cards can easily be seen as an unnecessary burden. Just recently I received a new SIM through the mail, which was a micro SIM housed in a standard SIM. The problem was that I needed a Nano SIM. Without a laborious and possibly fatal employment of rulers and sharp blades, I could not insert it into my phone. I had to call and have another SIM sent, costing me money and time.

different sim cards
From left to right: Standard, Mini, Micro and Nano SIMs. / © Cvdr based on Justin Ormont's work

For manufacturers, SIM cards are an obstacle to creating devices the width of a blade of grass, hence why SIMs have become so much smaller over the years.

The immediate question is why can't the data on a SIM card simply be stored on my phone?

The convenience of SIMs

As mentioned earlier, SIM cards are easily transferable. Assuming you have the right-sized SIM, it can be used in any unlocked device. This makes changing carriers and traveling abroad a lot more convenient. It also means it's more difficult for carriers to lock you into their service. While they may provide you with a phone that is locked, you can still get this unlocked after a fixed period and insert a SIM from any other carrier.

When the phone itself is used to tie you to a carrier, as with CDMA networks, breaking free becomes a lot more inconvenient.

eric galaxy s6 encryption
Unlocking a phone is a pretty simple procedure. / © ANDROIDPIT

But the security SIM cards afford is not to be sniffed at, either.

SIMs offer cryptography up to a level that is nigh-on impossible to attain in any other currently available fashion. They're extremely secure. For a start, you need the SIM, which is nigh-on impossible to copy, and you need the PIN. This is called two-factor authentification, which means there is something you have and something you know, much like having a bank card and knowing the PIN for that. Without both, there's no use in either.

mobile payment telekom maywallet credit card 07
SIMs use two-factor authentification, like banks cards. / © ANDROIDPIT

The alternative – having users log in with a username and password – is not only outdated in many respects, but would require passwords of absurd lengths to even begin to come close to the strength of security offered by SIM cards. Last year, head of the National Strategy for Trusted Identities in Cyberspace, Jeremy Grant, declared that "passwords are a disaster from a security perspective. We want to shoot them dead".

Housing the same data on the phone itself is not as secure as a SIM, either. Even a partitioned part of the internal storage set aside for the data is far more vulnerable to attack than a SIM card.

Do we need SIM cards?

Strictly speaking, no. CDMA networks operate without them, and there are other ways to achieve subscriber authentication. The fact is, however, that the way SIM cards do it is extremely secure and adaptable. The cryptography used by SIM cards is formidable as it is, and it is constantly improving.

While CDMA devices can operate without them, they will also only operate through the carrier you bought them from, making changing carriers a nightmare. SIMs make changing phones, carriers and countries as easy as it could currently conceivably be.

Similarly, the proposed eSIM, which Apple and Samsung are starting to pursue and which is effectively the same as a SIM, just integrated directly into the device – i.e. non-removable – would mean that there is no option to swap to another device with ease. It would require a visit, or, at least, a call, to your carrier.

You would be able to switch carriers with greater ease, depending on how many carriers support the format, but no longer would you be able to switch phones for a day or two, or when you're battery dies. The convenience of the SIM card in these scenarios is self-evident.

lg g4 sd sim
eSIMS would mean no more access to the card, making life harder. / © ANDROIDPIT

Do we want SIM cards?

From where I stand, the benefits of SIMs far outweigh any inconveniences they kick up. Security is to be valued in the tech world, and the SIM provides the most secure way of encrypting subscriber information and authenticating its legitimacy. Not only that, but the ease with which they allow you to switch devices and the roadblocks they present to carriers who wish to lock you into their services, are undeniably positive attributes.

I don't see the death of the SIM on the horizon, but I do see a changing approach to the way they work. You only need to look at the Apple SIM, which is designed to work across a host of international carriers through either short- or long-term data plans and is similar to something the GSM standards body has been working towards for some time now. The card itself, however, remains there to be removed at your leisure and to do its encrypting, authenticating job in any device you like.

Do you see SIM cards as a blessing or a burden? Have you tried going without one, or have you owned a CDMA device without a SIM before? Let us know in the comments.


Write new comment:
  • Dawn B. 9 months ago Link to comment

    I don't know why I have Two slots for sim cards

  • I think sim card are still something necessary if u are someome who travels a lot u can just simply swift cards and go on till u go back home put ur card back and thats it

  • Replacing a bad phone is simple with a SIM card. I see the lack of one as a limitation. It's just another way for carrier's and manufacturers to lock in a person to a device that maybe problematic or troublesome.

    Keep the card, maintain user flexibility.

  • storm 9 months ago Link to comment

    If you're a phone power user, eSIM is not in your interest.

  • Thanx for the article . I just hope that the so called eSIM dies a natural death as there goes buying a local SIM when traveling. LTE I believe came from the CDMA side of things as WCDMA did but was progressed thru the GSMA rather than via the CDMA alliance which is all but dead these days. Buy the way CDMA does have a SIM called uSIM that is used in places like China....

  • Very good explanation what is sim kard and why we need it; very usefol.

  • One of the best articles I've read here. Thanks Chris

  • Ellett 9 months ago Link to comment

    Any additional words on the SIMs used in Project Fi phones, which allow connectivity to dynamically switch back and forth between multiple carriers?

  • Thanks for sharing this useful info.
    It helped me a lot !

This website uses cookies to ensure you get the best experience on our website. More info

Got it!