What is an eSIM? The Apple Watch Series 3’s new SIM tech explained

The Apple Watch 3 is one of the first gadgets to use an eSIM. It lets you use the smartwatch like a phone, and it’ll even share your iPhone’s phone number, giving it that classic “it just works” Apple sheen.

But what is an eSIM? And how is it different from the normal SIM cards we all use in our phones? Allow us to explain.

What is an eSIM?

An eSIM is an electronic SIM card. As the name suggests, it will replace the physical, plastic SIM card all current smartphones use with a virtual embedded equivalent that cannot be removed.

The first time we came across this hardware in person was in the Samsung Gear S2 3G in 2016. However, we expect the Apple Watch 3 with mobile internet will shift a lot more boxes than that watch. The eSIM is going mainstream.

One of the benefits of an eSIM is that it’s absolutely tiny, just a small fraction the size of a nanoSIM. And they’re only the size of my pinkie nail.

This is what makes it so well-suited to ultra-compact gadgets like watches, which simply don’t have the room for a normal SIM.

An eSIM is non-removable, and sits by other internal components. You don’t have to remove it, and it isn’t at risk of compromising any water resistance of a gadget’s shell.

With such an embedded standard, the idea is that you can switch to a new operator without having to insert a specific SIM card. It’s all done through software.

The same Apple Watch 3 can be used by Verizon, T-Mobile or Sprint in the US. Only EE currently offers the Apple Watch 3 in the UK, so network switching isn’t an issue.

One of the most interesting aspects of the Watch 3’s eSIM is that it’ll share your iPhone’s number. You can think of them as part of the same connection. However, this also means it’ll only work with an iPhone – and that your iPhone and Apple Watch will have to be with the same network provider.

Related: iPhone X

The future of eSIMs

There’s more to the future of eSIMs than just smartwatches, though. Some believe we’ll one day seem them used in all phones.

The GSMA is the organisation that represents the interests of mobile operators around the globe, and it has announced a standard for this new kind of SIM.

Besides Samsung and Apple, AT&T, Deutsche Telekom, Etisalat, Hutchison Whampoa (owner of Three and soon O2), Orange, Telefónica (the current O2 owner) and Vodafone are also said to be on board.

The network data that a standard SIM card carries will be rewritable on future eSIM devices, so all you’ll need to do to change operator is make a phone call or two – rather like when you arrange to bring your phone number across to a new network now (though hopefully even easier).

Another advantage will be when travelling. It will be much easier to switch to a local network if you’re going to be spending any great amount of time abroad – particularly useful when travelling outside the EU, where roaming charges can be extortionate.

The other problem with physical SIM cards is that there are currently two or three sizes in play.

Have you ever tried swapping your iPhone for an Android phone, or vice versa? Very often, they use different types of SIM entirely. This necessitates the use of an ugly and flimsy plastic adaptor, or else an entirely new SIM, neither of which is ideal.

Related: Apple Watch 3 vs Fitbit Ionic


Apple SIM: Paving the way for the eSIM?

Apple actually offered us a glimpse at what eSIM integration might entail a while back.

Its 4G-enabled iPads incorporate something called Apple SIM. This is an entirely software-based SIM, which offered the freedom to swap operators at will.

Or rather, it did so in participating countries. The whole problem with the eSIM concept isn’t the technology, which has been viable for some time, but the cooperation of all the various parties – and that includes networks as well as manufacturers.

That’s where the GSMA’s new eSIM standard comes in – and fortunately for gadget fans, it looks like it’s starting to gain some real traction now following the Apple Watch 3 launch.

Related: watchOS 4 features

eSIM Summary: Ultimately, it’s about smaller phones

The final thing to know is that the Apple Watch 3 is just the tipping point for eSIM. Its true potential will only be unlocked – and noticed by the larger, smartphone-wielding public –when we see the first eSIM handset, as it’s likely to be slimmer than anything we’ve seen before.

‘Slimmer’, in the smartphone world, is usually associated with ‘better’, so expect this to be the moment that eSIM really hits the mainstream. Apple, as usual, will take credit for being at the vanguard of the technology – even if a rival did beat it to market with an eSIM device.

Why will eSIM help usher in the most svelte smartphones to date?

Well, physical SIM cards are deceptively simple things. They’re primarily useless plastic, with the actual ‘SIM’ part that little tiny gold strip you see on one side of the card. This means that doing away with SIM cards will free up a fair amount of extra space inside a phone, allowing manufacturers to reduce device girth by replacing it with a diminutive embedded equivalent.

It’s not just the space occupied by the SIM itself, either, but the housing, reader, and tray mechanisms that support it. With space at an absolute premium in modern smartphones, and every millimetre counting, the eSIM will help bring about even slimmer phones.

Depending on how eSIM goes down in the Apple Watch 3, it could well be that Apple’s 2018 iPhone is the first phone to sport the new-gen SIM tech – or that rival Samsung pips it to the post with next year’s Galaxy S9.

Related: Apple Watch 3 vs Apple Watch 2


Are you excited by the prospect of eSIM cards? Let us know in the comments section below.