If you’ve bought a new cell phone in the past decade or so, you probably already know about a SIM card — a small, thumbnail-sized card that you need to insert in order to connect your phone to your carrier’s and plan’s cellular network. They’ve been a staple of cellular technology for nearly two decades, but in recent years smartphone makers and carriers have begun to migrate to a new way of doing things: replacing the removable physical SIM with something called an eSIM.

In this case, the “e” stands for “embedded,” which makes sense because that’s a SIM card that stays inside your phone and can’t be removed. It performs the same function as a traditional SIM card but has the potential to make things simpler for most smartphone users.

What is a sim card?

SIM cards, short for Subscriber Identity Module, started as a core feature of the 2G GSM standard more than 20 years ago. We take SIM cards for granted today, but they were actually a breath of fresh air in an age when other cell phones had to be programmed directly with carrier information manually—usually by a technician in the store. In those early days, not all carriers supported SIM cards because they were not part of the competing CDMA cellular standard. However, SIM cards were such a great idea that GSM took over, 2G CDMA took off into the sunset, and SIM cards became an integral part of 3G and all the newer cellular technology that followed.

The SIM card is located in a special tray and slides into a device like a tray. It is usually provided by your carrier and preprogrammed with account information such as your phone number and security keys needed to identify and authenticate your phone on the carrier’s network. SIM cards can also store contacts and SMS messages, although these features are rarely used because today’s smartphones are much more powerful.

Without this card, your phone doesn’t even have a valid phone number, so you won’t be able to make or receive calls on a wireless network. The United States and many other countries require phones to be able to place calls to emergency services, even without a SIM card — but this is an exception.

This little card has a slit on one side with gold circles on one side that connects to a card reader inside your phone. SIM cards come in four different sizes — standard, mini, micro, and nano — so you need to make sure you get the correct size for the phone you’re using.

Most importantly, since the SIM card is removable, you can easily remove it from one device and insert it into another. This allows you to upgrade your phone without contacting your carrier. It’s also a great way to avoid roaming charges when traveling by setting up a pay-as-you-go service with a local carrier at your destination; Replace your regular SIM card, insert one from a local carrier, and you’ll have a new phone number on their network. You can often pick up prepaid SIM cards at airport kiosks and run with a local number minutes after you land.

However, the traditional SIM card is also a double-edged sword. As much as a removable SIM makes switching your service to a new phone, it’s also another part you’ll have to tinker with, and of course it can get damaged, lost, or even stolen—unless you take steps to set a PIN on your SIM (which can Being a hassle in its own way), anyone who gets their hands on your SIM card can take over your number and either incur charges on your account or receive text messages sent to you to break into your online accounts.

What is an eSIM?

Insert the embedded SIM card – also known as an eSIM. As the name suggests, this is a SIM card that is built into your smartphone and cannot be removed. It performs the same function as a conventional SIM card, except that it is programmable and attached (soldered) to your smartphone’s motherboard.

This may seem problematic at first. For example, when traveling abroad with phones with removable SIM cards, you can switch to another carrier’s SIM card to get local coverage and avoid paying roaming charges from your primary carrier. Likewise, if you want to switch local carriers while keeping your phone, a removable SIM card can be taken out and easily replaced with a new one in seconds. Your first impression might be that this is impossible with an eSIM.

However, eSIM technology makes switching carriers easier, at least in theory. Instead of waiting for a new SIM card to ship or making a trip to a local store to get one, you can make the switch right on your phone by entering information from your carrier—often just by scanning a QR code with your smartphone’s camera. If your smartphone has an eSIM in it, you’ll find options in Settings that allow you to configure your eSIM, switch between lines and carriers, and manage your accounts. If you’re using a dual SIM, eSIM technology can support multiple accounts – and switching between them is very easy.

Unfortunately, while getting an eSIM should be easier than getting a physical SIM card, this isn’t always the case. Some carriers have taken longer than others to embrace the smoothness of eSIM, and it’s not uncommon to come across a few who still want to mail you eSIM codes or have you visit a store before you can set up your phone. That takes away one of the biggest advantages of using an eSIM, but fortunately most carriers are working quickly to keep up with the times.

The other significant advantage of eSIM technology is the space that is saved by removing the physical SIM tray. Devices can be smaller because the eSIM is built into the device’s motherboard — there’s no unnecessary space taken up by placing a slot and tray on the outer edge of the device. This allows for thinner designs and larger batteries. It also helps improve water resistance by eliminating another place inside your phone for moisture to escape.

Devices with eSIM technology

The Google Pixel 2 ships with an eSIM that only supports Google Fi, while the Google Pixel 3 and later Pixel devices support third-party carriers. Samsung brought eSIM to its flagship smartphone lineup with the Galaxy S20, and Microsoft’s Surface Pro LTE was the first Windows 10 device to ship with eSIM technology.

Apple introduced eSIM in 2017 with the Apple Watch Series 3, the first LTE-capable Apple Watch. While the Apple Watch used eSIM exclusively, when the iPhone XS and iPhone XR debuted the following year, Apple added an eSIM to complement the physical SIM card slot and provide support for two phone lines. Apple also added an eSIM to the 2018 iPad Pro, though it did not remove the physical SIM card slot; The eSIM was introduced as an alternative for those who’d rather use that to set up their iPad for cellular service than a physical SIM card.

Apple continues to use a combination of a physical SIM and an eSIM in almost all iPhone models. However, last year, the iPhone 13 gained dual eSIM support, allowing users to have dual SIM support without the need for a physical SIM card. That set the stage for this year’s iPhone 14 lineup, as Apple has now completely removed the physical SIM card slot on US models, making eSIM the only way to activate your iPhone 14 on the carrier’s network.

iPhone 14 models sold in most other countries still have two eSIM cards and a physical SIM card slot, like the iPhone 13. The notable exception to this rule is China, where an eSIM is not built into the iPhone. Instead, when Apple first introduced the iPhone XS/XR in China, it provided two physical SIM card slots. This practice has continued to this day, even with the iPhone 14 lineup, which still has two physical SIM card slots in China — and no eSIM at all.

However, if you’re in the US and want a physical SIM card slot on your iPhone 14, there’s one thing you’ll want to keep in mind before moving to Canada or going down to Mexico to do some cross-border shopping. Although all North American iPhone models support the same frequencies of 4G/LTE, 5G Low Band, and 5G Midband, only US iPhone models support mmWave 5G used for the fastest parts of Verizon’s 5G Ultra Wideband and AT&T’s 5G Plus coverage.

When can I start using eSIM?

Chances are, your mobile device already has an eSIM, as we explained above. Laptops with cellular connectivity mostly connect using eSIM technology, such as the Surface Pro X and various models from Acer, Asus, Dell, HP, Lenovo, and Samsung. You’ll still see cases where SIM cards are used in laptop designs, but this is becoming less common.

Until eSIM technology becomes the global standard, many phones will still have a dedicated removable SIM card tray. There’s nothing wrong with using one of these phones — it’s just an old way of getting to know you on your carrier’s network. However, swapping a SIM card can be a hassle, given its size and delicate non-touch circuitry. Managing an eSIM is easier for everyone, whether you’re switching phones or moving to another carrier.

If you’re using a dual-SIM phone with a physical SIM card and an eSIM, such as an iPhone or Google Pixel, you may also be able to transfer your physical SIM information directly to the eSIM. Many carriers allow this, and iOS and Android provide tools to make it quick and easy. Once that’s done, you can get rid of your old SIM card and free up that slot for a physical travel SIM.

However, while you’ll want to check in advance, you might be pleasantly surprised to see how many international carriers support eSIM, and it’s hard to argue that it’s much easier to scan a QR code than trying to mess with a small, fragile code swap. A SIM card, especially when traveling through a busy airport.