How do SIM Cards Work, and Where Can You Buy Them? - Mobile Klinik

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How do SIM Cards Work, and Where Can You Buy Them?

person putting in a sim card into a smart phone

Whether you’re new to the world of mobile phones or have always been curious about the SIM card’s role in these devices, you’ve come to the right place. With modern-day technology, a SIM card is most commonly recognized as a small chip or digital card. It holds all the information it needs to connect you to a network. Explore our ultimate guide to all things SIM cards, where we cover what they are, how they work, how much they cost, where you can buy them, and much more. 

Table of Contents

What is A SIM Card?

SIM cards contain all the information needed to make it possible to connect with a mobile network. While some SIM cards have developed into digital software, the physical, tangible ones are what most people are likely familiar with. They are small plastic pieces with chips that contain processors and memory circuits for information storage.

SIM stands for Subscriber Identity Module. It stores two types of information: the Integrated Circuit Card Identifier (ICCID) and International Mobile Subscriber Identity (IMSI).

  • ICCID identifies the actual SIM card with an 18 to 22-digit code, which helps mobile network operators know which card is yours.
  • IMSI is a unique identifier that defines you as a subscriber in the wireless world, which includes the country and mobile network you belong to. 

In essence, a SIM card links your physical device with your account and enables you to make and receive calls and messages. The information stored helps service providers associate devices with your individual account so that you can use their network.

What Kind of Information is Stored?

SIM cards store data that is unique to you, like your identity, location, network, plan, phone number, personal security keys, stored text messages, and contact list. They also track data around making calls on your network, to other networks, and in other countries. This information includes how much you use the phone to make calls, send texts, or use the internet.

Is My Information Secure?

These tiny cards use encryption (encodes plaintext so only authorized parties can understand the information) to ensure all messages and communication are private. Encryption codes keep data secure and are used as proof that a phone is allowed to use a specific network. 

While SIM card technologies are designed to be secure, there are risks involved if hackers attempt to contact providers directly and fake your identity to get the card switched. More on this in the Advantages and Disadvantages section.

How do SIM Cards Work?

Generally, when you choose a mobile network provider in Canada, you sign on to an account plan that details how much data, calls, and texts you’ll get in exchange for a monthly payment. When you switch to this network, the provider will set up the plan by activating the SIM card, which they usually have on hand and can do right in the store.

When you connect your device to the service network, the operator will get an authentication key and the IMSI to verify that the device belongs to the user. Once this verification is confirmed, your device will get access to the network.

Types of SIM Cards

As technology has evolved, so have SIM cards. Generally, designs have become smaller to free up more space in the device and allow for more convenience and functionality. Here’s a quick walkthrough of the types of SIM cards over time:

Full Size

This SIM card debuted in 1991 and is the first and biggest of all the types; comparable to the size of a credit card. Full-size SIM cards generally are not in circulation anymore but were common in older mobile phone models from the 1990s.


Released in 1996, the mini SIM had a reduced size compared to the original version — about one inch long. These were commonly used in early devices from the late 1990s to the early 2000s, like the iPhone 3GS. Although rarely used now, you can still find standard SIMs if you have these older models laying around.


The micro SIM is smaller and has less plastic than the standard. It was released in 2003 and is commonly found in phones from the early to mid-2010s, like the iPhone 4 and Samsung Galaxy J7.


The nano is the physical SIM card most of us are familiar with today. Introduced in 2012, this card is 8.8 by 12.3 millimetres (0.34 by 0.48 inches), making it the smallest removable one to date. Modern Android and iOS devices, like the iPhone 5 and newer, are compatible with this card.


This revolutionary technology, released in 2016, removes tangibility altogether. An eSIM is embedded in your phone and can’t be removed. The embedded technology has software built into the device, allowing you to activate a plan with a service provider without needing a physical card. It’s the first entirely digital SIM of our time!

New phones, like the iPhone XR or later and the Samsung Galaxy S20 or later, support eSIM, but these devices usually include a removable SIM card slot just in case. Since it is even smaller than the nano, eSIM technology also appears in wearables like Apple Watches and Samsung Galaxy Watches. 

Here are some of the main advantages of an eSIM:

  • It makes changing networks and plans easier because you never have to change the card.
  • It can support multiple networks and numbers at once. For example, you can install eight or more eSIMS on an iPhone and use two numbers simultaneously, according to Apple.
  • SIM management is conveniently facilitated through your phone’s settings, so no physical work is required.

Dual SIM

Smartphones with Dual SIM technology allow you to have two different SIM cards simultaneously on the same device, which means you can have outgoing and incoming calls or text messages from either one on the same phone. Typically, dual SIM is available with nano or eSIM combinations. 

This technology is typically only compatible with higher-end, modern devices, like the Samsung Galaxy S22 series. For iPhones, you can:

  • Use dual nano SIM if you have iOS 12.1 or later and an iPhone XR to iPhone 13
  • Use two eSIMs or a combination of nano and eSIM for later models. 

Dual SIM benefits people with two phone numbers (like a personal and work cell) who don’t want different phones. This can also come in handy for travellers who wish to use one SIM for their home network and the other during international travel. Tri-SIM or multi-SIM options are also popular, allowing more than two numbers at a time. 

Where to Buy a SIM Card

In Canada, you will get a SIM card when you sign on to a plan with any service provider. If you are travelling to the country, you can also purchase prepaid SIM cards from these operators. SIM cards are also available at:

  • Gas stations
  • Convenience stores
  • Amazon
  • Big box stores like Best Buy
  • Professional repair shops, like Mobile Klinik

When travelling, some people choose to buy an eSIM card through an online store like Holafly or Airalo because this allows you to connect to the local network of your destination the moment you land. Even airports sell SIM cards, although these are known not to be the best value for your money.

How Much is a SIM Card?

How much a SIM card costs depends on where you get it and your purposes. For example, if you live in Canada and are signing onto a plan with a network provider, purchasing a SIM card often does not come with an extra charge. However, depending on the operator, you may face activation fees. 

On the other hand, if you’re travelling to Canada or live in the country and want to sign up for a prepaid plan, you’ll likely require a prepaid SIM card. Prices can differ between brands and types of cards but generally range around $10. Prepaid SIMs are available at any of the stores mentioned above.

Advantages of SIM Cards

In reality, using a phone without a SIM card will not get you very far. SIM cards are necessary in most cases if you want easy access to phone calls and text messages. Let’s take a look at some of their advantages.

  • Allows you access to a local network: A SIM card helps you stay connected with your contacts and use your phone whenever necessary.
  • Makes travelling easier: Instead of paying high international roaming rates from your domestic provider, you can purchase a SIM card from an operator in the country you’re travelling to for a lower price and easily switch back when you return home. Keep in mind that switching SIMs is only possible if your phone is unlocked.
  • Easy data transfer to your new devices: If your phone suddenly stops working or you decide to get a new one, you can easily switch your SIM card to a different phone and receive calls and messages.

Disadvantages of SIM Cards

Here are some disadvantages of SIM cards to be aware of:

  • Easily Misplaced: While less of an issue with an eSIM, a nano SIM can be easily lost, mainly because of its size. It’s important to keep careful track of where you put it if you decide to take it out and switch to a different one temporarily.
  • Inflated prices while travelling: As outlined above, purchasing a SIM card from your destination country can be cheaper. However, if you decide to keep your original card when you travel or if you’re locked in with your domestic provider, international charges can become very expensive, depending on where you’re visiting. This may result in a hefty bill upon your return home. 
  • Potential security threats: While SIM cards are designed for security with data encryption, it’s possible that attackers can access this data by calling your service provider, faking their identity, and pretending to be you. If they make it through the authentication questions, they can transfer your account to a new SIM card.

The good news is that if a fraudulent SIM swap is successful, you’ll know pretty quickly because your phone will no longer be able to send or receive messages or calls. Once these suspicions are on your radar, the attackers will have a limited amount of time with the data they acquired, but this doesn’t mean they can’t do any damage during this time. 

To prevent hackers from accessing your account and impersonating you, set up a PIN or password connected to your mobile account. Ensure you keep this PIN safe where no one can access it. 

How to Replace SIM Cards

Physical SIM cards can be easily removed once you locate where it is on your phone. Some models place it near the battery, requiring you to open the back panel. Other models have an insert on the side of the phone which can be opened by pressing the hole with the point of a paper clip.

Removing an eSIM is even easier. Simply go into your settings, tap “Cellular” on an iPhone or “Mobile Network” on an Android and select the eSIM profile you want to erase. Of course, because this is an embedded technology, everything is done through digital software — no physical labour is required!

How do SIM Cards Work While Travelling?

As discussed previously, SIM cards only work with their respective network operator. If you’re travelling outside your home country, your SIM card may work overseas, but this would require you to opt into international roaming. If you don’t choose to keep your original (domestic) SIM card while going abroad, you will need a new one from a provider that operates in the location you’re visiting.

Travelling Outside of Canada

If you’re travelling to the U.S., many Canadian service providers offer roaming plans for a fee. This rate often differs from other international destinations. Check with your provider to see what options they offer. For example, Telus and the other main networks in Canada offer roaming plans in the United States for $12/day and international roaming for $15/day. 

Keep in mind that not all countries are included in international roaming plans, so do your due diligence and confirm that your destination is on this list before taking off. 

Alternatively, you may find cheaper options than international roaming plans. You can buy a SIM card from an operator in your destination country and use your phone on their network. It’s important to note that in most cases, this option requires that you have an unlocked phone. To unlock your device, you can do it yourself or ask your network provider. Thankfully, as of December 2017, the Canadian Radio-television and Telecommunications Commission (CRTC) prohibits charging a fee for this service, and all devices offered after this date should be already unlocked.

Travelling to Canada

If you’re from the U.S., your mobile provider may offer roaming options in Canada, typically with a fee for each day you’re away. If you’re from other international destinations, check with your provider to see if there are any roaming options for you. In this case, buying a new SIM card may not be necessary.

However, buying a prepaid SIM card could be the easiest and cheapest option. You can do this by visiting one of Canada’s many network providers, like Telus or Koodo, upon entry into the country or buying a prepaid eSIM online to connect with the network as soon as you land. Online stores that offer this option include Airalo, Holafly, or Nomad.

Frequently Asked Questions

Do you have more questions about SIM cards? Here are some answers to frequent asks to help you out.

What happens if I don’t have a SIM card?

If you don’t have a SIM card or it has yet to be activated, you can’t get incoming or outgoing calls or texts or access the network. You’ll only be able to use your phone with Wi-Fi and access your camera. In North America, every smartphone is required by law to be able to call emergency services (911) without a SIM card or plan.

Will phones always need a physical SIM card?

As outlined previously, as technology evolves, more carriers and smartphone manufacturers are embracing eSIM software with the same capabilities without the hassle of a physical card, which can get lost easily. This means that, eventually, manufacturers may design smartphones without a slot for a card.

Are all SIM cards the same?

No. Depending on where you purchase your SIM card, some are specific to the carrier you buy from. In this case, you can use the SIM card on any phone that the network provider supports. But, if you want access to a different network, you may need to purchase a different one. 

Is it easy to get a SIM card?

Yes. Most modern phones come with a SIM card in them, ready for activation. However, it’s easy to go to any carrier and ask for a new one. They will even activate it for you. As mentioned previously, you can get SIM cards pretty much anywhere — from network providers to online and big box stores.

Does my phone need to be unlocked?

If you want to get a new SIM card for a different number or travel, your device needs to be unlocked from its home network to use a foreign SIM card. Since the federal Wireless Code changed in 2017, all devices offered after this date should be unlocked, regardless of your contract with your Canadian service provider. 

If your device is locked, your provider should be able to unlock it for free, as outlined by the same Code amendments. Alternatively, you can see if your provider has international roaming plans, but remember that these can be expensive. Unlocked devices are free to use on any network worldwide by purchasing a SIM card (which will include a local number and plan) from the international carrier or an eSIM from an online store, as outlined above

To see if your device is unlocked, check your settings. On iOS devices, go to Settings > General > About and scroll down to Carrier Lock. If it says “No SIM restrictions,” then you can switch your SIM. If this field displays a carrier name, your device is locked. On Android devices, the steps may differ, but generally, you can go to Settings > Connections > Mobile Networks > Network Operators. If multiple carrier names appear, this may indicate that you have an unlocked device. You can also check by replacing your current physical SIM. If the new one can make calls, there are no restrictions.

The Future of SIM Cards

SIM cards will likely be part of our mobile world for the foreseeable future. It may become more common, though, for you to have multiple SIM cards with different providers on one phone at one time (see dual SIM technology).

As smartphone technology evolves, eSIMs will likely become the most-used type of SIM card because they are convenient, and you don’t have to worry about losing an eSIM every time you switch your account.

SIM Cards with Mobile Klinik

Are you in need of a new SIM card or phone plan? At Mobile Klinik, we sell Public Mobile SIM cards in-store and can guide you through the activation process. It’s simple and easy — we’ll help you set up your account and walk you through the steps of getting a new phone number or transferring an existing one. If you have more questions about SIM cards, require a phone repair, or need a new device, we have you covered! Visit us at any of our locations across Canada. We take appointments and welcome walk-ins.

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