What is a SIM Card?


If you own a cell phone, or have been thinking about buying one, you’ve probably heard of SIM cards. Unfortunately, they tend to come up in conversation most often when they’re not working!

“I can’t make calls – my phone doesn’t have a SIM card.”
“I lost all of my contacts when my SIM card broke.”

These kinds of ominous statements might leave you wondering… what is a SIM card? And do I need one?

The Basics

Essentially, a SIM card is a form of personal identification between you and your mobile provider. See, a mobile network is an extremely valuable commodity, but it’s not something that can be locked away in a safe somewhere. It’s floating in the air, and without SIM cards, anyone would be free to use these mobile networks without paying.

Your SIM card, once activated, lets the phone company know who you are and that you should indeed have access to their network. When you turn on your phone, your SIM sends information to your phone or device about which network to connect to. It also provides the security credentials you need in order to safely connect. (Though you can always make emergency calls with any device, regardless of whether it has an active SIM card.)

SIM cards also store your contacts, messages, and other data.

Standard, Micro & Nano SIMs

Don’t let these terms confuse you as you come across them in your research – they’re all describing, in essence, the same SIM Card!

Standard, micro, and nano simply describe the physical size of the card itself. Newer devices, like the iPhone 5, use the smaller, nano SIM in order to accommodate a narrow body. Older models and some larger devices will use either standard or micro SIMs.

Do I Need a SIM Card?

You might. But if you do, your phone almost always comes with one.

Let us explain.

There are essentially two types of consumer phones: GSM and CDMA. The technical differences between the two are many, and we could spend an entire blog post discussing the intricacies of both (maybe we will some day soon!).

But for the purposes of this post, all you need to know is that GSM phones require SIM cards, while CDMA phones don’t. Instead of SIMs, CDMA carriers (think Sprint & Verizon) keep a list of all the phones that are allowed to use their network and use serial numbers to authorize network access.

If you sign up with a GSM carrier (most carriers besides Sprint, Verizon, and their partners) and buy a GSM phone, your phone will almost certainly come pre-loaded with its own SIM card, ready for your use.

What Are The Benefits of SIM Cards?

So we’ve established that SIM cards can broken or lost, taking all your data and network access with them.

Why not just go for a CDMA phone and avoid the headache altogether?

It all depends on your needs as a mobile user.

CDMA phones feature internal storage and card-less access to your mobile network, but offer far less flexibility than GSM (SIM card) phones. When you want to change CDMA phones, it can be a pain extracting your contacts and data from the old device. CDMA phones also are notoriously useless when it comes to international travel.

GSM phones, on the other hand (and thanks to those handy SIM cards), allow you to easily transfer your “mobile identity” from one device to another, just by transferring the card itself. These devices also open up new possibilities for international travel and tapping into mobile networks while abroad.

Update – 02.10.2015

Just when we thought it was simple, the ever-changing world of mobile technology is here to switch things up on us! Recently, we’ve come across a term that needs to be added to our SIM card resource. Does UICC ring a bell?

You might have heard of a UICC in reference to your phone’s SIM card, as it’s used by all networks that operate on LTE. A UICC stands for Universal Integrated Circuit Card, and it ultimately works just like a SIM! That means it’s a form of personal identification between you and your mobile provider that allows you to have access to their network. UICC replaced the term SIM when 3G networks were introduced.

Modern UICC cards have two “applications”. One is a SIM Application so your phone can work with older technology (also known as being backwards compatible). The other is called a USIM Application, and is what authorizes your device to operate on 3G/4G networks.

It’s worth noting that consumers typically just refer to UICCs as SIMs, since the terms are really just tech-talk and the difference doesn’t affect every-day use. But we’re here to help you fully understand the mobile phone market. So next time you hear UICC, go on and join the conversation!

Wrapping Up

Whether or not you’ll need a SIM card, and whether you choose a GSM phone or a CDMA phone, depends on your individual needs. How much flexibility do you need? Will you be switching devices often? Will you be travelling abroad?

To learn more about the different available mobile phone options, take a look at which devices we offer.

If you have further questions, let us know in the comments. We’re happy to continue the discussion!

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