The Best GSM SIM Cards

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How to Find the Best SIM Card for Your GSM Phone

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You have probably heard of inserting your SIM card when activating service with your carrier, no matter the device. It could be your phone, your tablet, or whatever - it's a useful piece of universal equipment.

However, what exactly is a SIM card? Furthermore, since SIM cards are both used by GSM and CDMA networks, what are GSM and CDMA networks? Which MVNOs are compatible with GSM SIM cards?

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Hence, this article. Not only will you find information regarding what MVNOs are compatible with the GSM network, but you'll also learn more about the SIM card, the difference between GSM and CDMA, and information regarding the Internet of Things.

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What Is a SIM Card?

First thing's first: you're probably unsure as to what a subscriber identity module card is.

Well, a subscriber identity module (SIM) card is a type of smart card that is made for mobile devices. More or less, this tiny card sports your unique identification number, your personal data such as contacts, and more. This card helps you connect with your mobile phone provider and allows you to participate in its network. However, if the mobile SIM card is removed from the SIM card slot, then service will be discontinued.

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In other words, a SIM card lets the mobile operator know who you are and whether or not you have permission to access the network with your phone number and other credentials.

There are, of course, different sizes of mobile SIM cards. Depending on your cell phone model and the size of the SIM card slot, you may need a standard SIM, micro SIM, or nano SIM card. The standard SIM represents the second generation of SIM cards, measuring 25mm x 15mm x 0.76mm. The micro SIM is the third generation of SIM cards, measuring 15mm x 12mm x 0.76mm. Finally, the nano SIM acts as the fourth generation of SIM cards, measuring at 12.3mm x 8.8mm x 0.67mm.

Switching Providers

When you want to switch providers and would like to bring your own phone, then you'll probably be forced to unlock your phone's SIM card. Fortunately, the SIM unlocking process is simple. You may have to have your carrier unlock your phone, but sometimes your carrier won't. After all, some carriers may have rules to see who is qualified for a SIM unlock code. For instance, you may still owe money on your phone, so they won't want to give up the unlock code. Fortunately, you can always contact an unlocking service.

International SIM Cards

International SIM cards are a great option if you're a constant traveler (otherwise we would recommend the local SIM card). With an international SIM card, you'll receive coverage in the specified location. Furthermore, sometimes you may receive low international rates with the international SIM card.

GSM and CDMA? What's the Difference?

GSM and CDMA are two different mobile phone technologies. GSM stands for Global System for Mobile Communications. CDMA, on the other hand, stands for Code Division Multiple Access. GSM is more globally accepted compared to CDMA. But what's really the difference? Basically, the difference lies in the method of radio wave conversion - the same radio waves that your cell phone broadcasts.

GSM divides the frequency bands so that more than one user can dial a phone number using a tower simultaneously. CDMA networks, on the other hand, layer digitized calls over each other and unpack them on the back end thanks to the issuance of sequence unlock codes.

But who exactly relies on what technology?

Verizon and Sprint both rely on CDMA technology, while AT&T and T-Mobile networks use GSM technology. So expect GSM SIM cards with AT&T and T-Mobile networks, but CDMA SIM cards with Verizon and Sprint for your CDMA phone.

Which MVNOs are Compatible with the GSM Network?

Below, you'll find a list of the MVNOs that are compatible with the GSM network. With a GSM network, you'll need a prepaid SIM card. Some MVNOs offer a free prepay SIM card, whereas others will have you pay for a SIM card.

There are dozens of GSM-compatible MVNOs, but the above are just a few of our favorites.

Internet of Things

As you might have noticed, more devices are being connected to each other. This is known as the Internet of Things.

The Internet of Things is the inter-networking of physical devices, vehicles, buildings and other items embedded with electronics, software, sensors, actuators, and network connectivity which enable these objects to collect and exchange data.

One such example happens to be smartwatches being connected to the smartphone - for instance, the Samsung Gear S2 interacts with the Samsung Galaxy phone series or the Apple iPhone 7 with the Apple Watch or the Apple iPad. All of these devices rely on each other thanks to the exchange of useful information. Another relevant example is SIM cards, and how they are not only used in smartphones but also in tablets, GPS trackers, smartwatches, and more. In other words, your SIM card is a valuable piece of plastic, containing your unique identity within these items.

Not only that but carriers like US Mobile and TPO offer SIM cards specifically for non-smartphones. You'll notice at times when you bring your own phone to a GSM network that you'll need a GSM phone. So be sure to check whether or not you have a GSM phone or CDMA phone with the carrier's official network compatibility page.


As you can tell, there are plenty of mobile providers that rely on GSM technology and SIM cards. Overall, it's best to be certain that, when you select a GSM network, that you have a GSM-compatible phone. Otherwise, you'll have to purchase an unlocked phone from a retailer or a phone directly from the provider, which could cost you.

SIM cards are useful for giving a data plan to a plethora of devices such as activity trackers, alarm systems, smart watches, and more. For more information, reviews, and comparisons check out our connected devices directory. If you need a device with a 4G LTE connection specifically, check out our comparison guide here.

Looking for CDMA SIM cards instead? Go here.

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