Two Hologram sim cards sitting on a countertop

What is a SIM Card and Why Do You Need One?

A subscriber identity module (SIM) card stores data about its user (whether that user is human or machine) including the international mobile subscriber identity (IMSI) number and its key. The IMSI is used to identify a specific line of service that the user’s data plan is attached to. Every SIM card also contains an integrated circuit card ID (ICCID), a 19- or 20-digit number that’s typically printed on the back. The ICCID is a globally unique serial number that serves as a signature to identify the card. Some SIMs also store contact information and even run software.  

Ultimately, the SIM serves as a link between a cellular device and a network. It’s the identification card, if you will, that allows a device to join a network and send and receive data. Every cellular device, whether it’s a consumer smartphone or  an IoT sensor, needs a SIM.

To jump to what you need, click the links below:

A Brief History of SIM Cards

What Does Dual SIM Mean and How Does It Work?

What is an IoT SIM Card?

What is a SIM Form Factor?

How Do I Choose the Best Type of SIM for My Device?

SIM Card Form Factors for IoTeSIM vs. Nano SIM

Factors to Consider When Choosing a SIM

What Should I Look For in a SIM Card Provider?

A Brief History of SIM Cards

SIM cards appeared in the early 1990s with the advent of mobile phones. Developed by German company Giesecke+Devrient, the early SIMs were used by Radiolinja, a Finland-based wireless operator, to make the first GSM phone call in 1991. The size of a credit card, these SIMs supported 32 to 128 KB of data and had the ability to store a modest number of contacts and SMS messages. Five years later, mini SIM cards came on the market in 1996 and provided a more compact solution for shrinking cellular phones. Many of us remember switching out a SIM card when upgrading to a new phone, bringing our contacts and saved messages with us. 

When smartphones came on the scene, SIM cards became even smaller. The Micro SIM appeared in 2010, and the Nano SIM in 2012. As IoT devices came on the scene, embedded SIMs (or eUICC-enabled eSIMs) started to become available. Because they’re built into the device and can be provisioned remotely, eUICC-enabled eSIMs are a helpful innovation for IoT deployments at scale. 

What Does Dual SIM Mean and How Does It Work?

Some devices have space for two SIM cards—thus the term “dual SIM.” A dual SIM device can hold two SIMs with their distinctive identities, network settings, and lines of service. Usually, only one SIM can be active at a given time, but the device operator can switch between them as needed. For example, a phone might have one SIM for the user’s business number and contacts, and another for personal use. Or an IoT device might have one SIM for use in North America, while another allows it to connect to networks and services in Europe.

What is an IoT SIM Card?

Much discussion of SIM cards centers around their original (and continued) use in mobile telephones. But in recent years, distinctive machine-to-machine (M2M) or IoT SIM cards have emerged. Unlike a traditional SIM, an IoT SIM card sends and receives data rather than making voice calls. IoT SIM cards have more memory and durability than their consumer counterparts, and they also last longer—up to 10 years or more. And they can tolerate environmental challenges like vibration, corrosion, and extreme temperatures.

IoT SIM cards operate in much the same way as traditional SIMs, storing unique information such as the IMSI and carrier data and serving as the link that authenticates and connects the device to the network. But IoT SIM cards don’t require human interaction on the device side to activate, making them more flexible and independent than traditional SIMs. And today, some IoT SIMs include eUICC technology, meaning that network operators can switch out SIM profiles for a particular device from afar, rather than sending out personnel to find the device and swap out a physical SIM card.

What is a SIM Form Factor?

SIM cards come in various sizes or form factors. When the first SIM cards appeared, there was only one form factor: the credit-card-size 1FF. Today, there are four standard sizes of removable SIMs, along with the embedded SIM (MFF2). As mobile phones shrank over the years, so did their SIM cards. IoT SIM cards come in the same form factors as traditional consumer SIMs.

How Do I Choose the Best Type of SIM for My Device?

Form factor is just one element of choosing the right SIM for your IoT (internet of things) device. The best decision depends mainly on the size of the device and how much space can be allotted to the SIM card. It’s important to note that the chips themselves are the same on form factors 2FF–4FF—the difference is in the size and thickness of the surrounding card.

SIM Card Form Factors for IoT

  • Mini SIM (2FF)
  • Micro SIM (3FF)
  • Nano SIM (4FF)
  • Embedded SIM (MFF2)

Mini SIM (2FF)

At 25mm x 15mm x 0.76mm, the Mini SIM is the largest removable SIM card currently in use. It’s been around since the mid-1990s, when it emerged as a smaller option (at the time) for shrinking mobile devices. Today, the Mini SIM still works well for larger connected devices, like cars and vending machines.

Micro SIM (3FF)

The Micro SIM measures 15mm x 12mm x 0.76mm, significantly smaller than the Mini SIM. It’s large enough to be manageable for easy physical swapping of SIM cards, but it fits better in mid-size IoT devices like tablets and telehealth monitors.

Nano SIM (4FF)

Measuring at 12mm x 8.8mm x 0.67mm, the Nano SIM is both smaller and slimmer than its counterparts. It’s an ideal solution for compact IoT devices including wearable technology and mobile payment equipment. 

Embedded SIM (MFF2)

The embedded SIM or eSIM is soldered directly to the device’s motherboard, so it’s fully encased in the device. That means it’s a great choice for IoT devices deployed outdoors or in harsh conditions. For large-scale deployments, choosing an eSIM can also simplify your supply chain because it removes the step of physically installing a SIM in every device. There’s often confusion around the term eSIM, as many people use it to refer to eUICC-enabled eSIMs. But the eSIM itself is simply what it claims to be—an embedded SIM—and does not automatically enable remote provisioning. More IoT designers are starting to embrace eUICC-enabled eSIMs, though, because of their versatility and flexibility. (For more on that, check out our eUICC SIM platform, Hologram Hyper.)

eSIM vs. Nano SIM

There’s also some confusion around the eSIM and the Nano SIM, perhaps because they’re both compact and represent up-to-date technology. The Nano SIM has become ubiquitous in Apple iPhones and other smartphones and is used in many IoT devices as well because of its unobtrusive size. But while the Nano SIM functions just like a traditional removable SIM card, the eSIM is inside and permanently attached to the device. If the eSIM is eUICC-enabled, you can switch out identities via over-the-air (OTA) remote provisioning.

If you’re designing an IoT device and unsure whether the Nano SIM or eSIM is a better choice, think about:

Device Accessibility

Once deployed in the field, will the device be easy to access should you need to switch out the SIM card? For example, if you’re designing an IoT sensor for smart farming applications, some sensors might end up far out in a cornfield. If so, the eUICC-enabled eSIM’s ability to switch out SIM profiles remotely could come in handy.

Coverage

Coverage is another variable to consider. Dual SIM devices can switch between physical SIMs, but eUICC-enabled eSIMs can store several additional SIM profiles, making it easier to switch data plans and network providers. This is important if, for example, you’re creating an asset tracking device that will travel cross-country onboard a tractor-trailer.

Factors to Consider When Choosing a SIM

When matching your device with the perfect SIM form factor, size and accessibility are the main concerns. Larger devices can accommodate the bigger SIM form factors, while smaller devices demand the tinier ones. Beyond those basics, here are a few other considerations to keep in mind:

Protective Casing Differences

While its slenderness is an advantage for some applications, it also means the Nano SIM lacks the protective layer of plastic around the contact chip that the other removable form factors have. For that reason, the Nano SIM might not be the best SIM technology for IoT devices that are exposed to extreme temperatures or weather conditions. For devices deployed outside, underground, or in otherwise damaging environments, the eSIM provides an ideal solution since it’s sealed within the device.

Security Concerns

Depending on the location and circumstances of the deployment, some IoT devices will be at higher risk of security breaches than others. Removable SIM cards have historically been a point of vulnerability as bad actors can take one from a device like a scooter, and attempt to use it on a phone or tablet to connect to the Internet. IoT SIMs equipped with multi-factor authentication guard against security breaches by using key rotation, signing, and message authentication codes to verify an IoT device’s identity and secure its communications. These security safeguards stop hackers from ripping the SIM to stream Netflix or scroll social media. And some IoT platforms, such as the Hologram Dashboard, allow you to trace the location of SIMs, matching them against the device’s International Mobile Equipment Identity (IMEI) and notifying you with an alert if the SIM turns up in a different location than the IMEI. When you choose a SIM for your device, look for security features such as these to offset potential risks.

Remote Provisioning Abilities

As IoT deployments expand around the world, more organizations are looking for remote provisioning abilities in their SIMs to allow more efficient and flexible connectivity. eUICC-enabled removable SIMs and eSIMs can both provide this capability, allowing operators to swap out subscriber profiles using a method called Remote SIM Provisioning (RSP). Whether or not you need RSP is a question to pursue with your design team, but there are several benefits of building with eUICC—for example, it enables a single SKU to work for multiple deployments around the world and gives you the ability to update SIM profiles after devices are deployed. If your deployment is large, these advantages could yield significant savings in effort and costs.

What Should I Look For in a SIM Card Provider?


No matter which SIM form factor you choose for your device, you’ll want to make sure it can provide the longevity, durability, and global connectivity you need for your deployment. Depending on your use case, look for a SIM card provider that prioritizes:

Connectivity

Connectivity is an essential element for any successful IoT deployment. Find an IoT SIM card provider that can support flexible, global connectivity for your devices. Some providers today are carrier-agnostic, meaning they’re able to use the best available network no matter where the device is in the world. If the device is in motion, the SIM can automatically switch between carriers to maintain top performance.

Scalability

Choosing a carrier-agnostic IoT SIM can help you scale faster, but there are some other details that also play a role. A SIM that’s also hardware-agnostic can be paired with any device and connect to any IoT cloud service. Also look for a provider that streamlines integration with existing systems and allows your developers to build custom apps and dashboards. For example, Hologram’s powerful REST APIs help you integrate quickly.

Platform Performance

Look for an IoT SIM provider that includes an easy-to-use device management platform—something that you can get up and running quickly and won’t spend weeks trying to learn. A good device management platform should have customizable dashboards, role-based access control for security, and a 24/7 support channel in case something goes wrong (at some point, it inevitably will). It’s also smart to look for a provider that makes regular updates and upgrades to their platform, and keeps track of potential security threats.

eUICC Capabilities

Even if you’re not ready to implement an eUICC-enabled eSIM in your current device design, it’s worth finding a provider who can support them should you decide to go that direction later. That way, you won’t have to find an additional provider or switch providers if you want to enable remote provisioning in future product models.

Clear Pricing

Traditional M2M data plans often require up-front contract commitments and fees for activation, de-activation, or changes of plans. If you’re starting small but want to scale, look for a provider that will allow you to do so in a cost-effective way—rather than paying for more than you need. For example, Hologram uses a flexible pay-as-you-go model, with clear pricing and rates that adapt as you scale up. You won’t need to sign a contract or fill a quota.

Hologram makes IoT SIM cards in all form factors, including the eSIM (MFF2). Our hardware-agnostic global SIM card or chip allows you to connect to every network in every country and automatically switch carriers to make sure your device has the best available service (2G, 3G, 4G LTE, and CAT-M1), wherever it may be.

On the management side, you can keep track of your devices using either the Hologram Dashboard, which provides simple collaborative management tools to oversee device health, IoT connectivity, and security, or through our modern REST API.

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