We could see phones and networks adopt electronic SIM cards for future smartphones - essentially removing the need to have a physical SIM card (and SIM slot). 

Apple has turned to eSIM to add connectivity to the Apple Watch Series 3 and Watch Series 4 as well as dual SIM support for the new iPhone XS and XS Max. Google's Pixel 2 also supported eSIM but it was only used in the US for Google's Project Fi. 

The use of eSIM brings a number of advantages to device manufacturers and networks, but there's also some advantages for you, too. You could use one number for business and another number for personal calls or have a data roaming SIM for use in another country. You could even have totally separate voice and data plans.

But what exactly is an eSIM? And what exactly will it offer if your next device supports it? Let us explain more.

What is an eSIM?

The term "eSIM" simply means an embedded SIM card. There are no physical SIM cards involved and no physical swapping over required by you.

eSIM needs to be supported by the network or carrier and enabled by them, so for your new iPhone XR, XS or XS Max you'll need to choose an eSIM-compatible network for the second SIM support. 

An eSIM is basically a small chip inside your phone and works in a similar way to the NFC chip inside your phone. 

The information on an eSIM is rewritable, meaning you can decide to change operator with a simple phone call. They're really easy to add to a data plan – connecting devices with eSIMs to a mobile account can be done in minutes.

Note that there is also a physical SIM slot in the XR, XS and XS Max - the eSIM inside these handsets is used for the second SIM support. 

eSIM is backed by the GSMA, the association of mobile networks. The GSMA has defined the standard for eSIM worldwide. 

When is eSIM coming? 

eSIM will be available from many carriers. With iPhone XS and XS Max you'll either need to have a carrier's app or a QR Code you can scan. Again, the carrier will need to support eSIM.

In this UK the carriers will include EE who said in a statement to Pocket-lint "this functionality will be available shortly after the launch of the new iPhones. We asked whether eSIM would be enabled via the EE app and were given the short answer: "no". So expect to have to go another route (QR code?) to add an EE eSIM to your handset. 

In the US, AT&T, T-Mobile USA and Verizon Wireless support eSIM. 

Global mobile network Truphone today will also be offering data plans on the iPhone eSIM. These will be able to be bought via the MyTruphone app when the device is available. You're able to pre-register to find out more information, too. 

Truphone's international plans work across 80 countries including in Europe, the Americas and Australasia. 

eSIM is great for regular travellers

Theoretically, eSIM should mean that you could go to another country and simply add a roaming eSIM to your handset while retaining access to your main "home" number. That's one of the disadvantages currently because, if you change SIMs abroad, for example, you can't access your own number.

“eSIMs have the potential to eliminate roaming charges abroad", says Truphone's Steve Alder. "It also enables people to switch operators quickly to get connected if they’re in an area with no signal, frees up space for new features or additional battery life and could lower the risk of device theft.

"As consumers and operators begin to see the benefits, mass adoption of eSIMs will be inevitable.”

What does eSIM mean for devices?

One of the advantages it offers from a design point of view is that you make a smaller device because there's no need to accommodate a SIM card or the tray that holds it. There's also no need for networks to manufacturer or distribute lots of SIM cards. 

eSIMs will also be great for other devices like laptops and tablets, where seamless connectivity will become the norm. 

Vodafone says that eSIMs will enable more connected devices simply because eSIMs don't require so much room inside a device, enabling fitness trackers or even glasses to have stand-alone 4G connectivity in a way they just weren't able to before.

How will eSIM work in practice? 

We spoke to EE to ask how it will work with eSIM on the new iPhone XR, XS and XS Max. The network told us that if you have a physical and eSIM provisioned and are connected to two separate networks, your iPhone will display both networks on the screen at the same time.  

If the handset is in standby and both the SIM and eSIM are provisioned, customers will be able to receive calls and texts on both numbers. You then choose a “default” line that you make calls on, use SMS and that iMessage and FaceTime use. The other line is just for SMS and voice. 

Alternatively you can choose to Use Secondary for cellular data only - useful if you're abroad and using a local data eSIM. 

You can store more than one eSIM in your iPhone, but you can use only one at a time.

You can switch eSIMs by tapping Settings > Cellular > Cellular Plans and tapping the plan you want to use. If you are in the UK it's Mobile Data. Then tap Turn On This Line.

How to use eSIM with iPhone XR, XS and XS Max

If you have a QR code:

1. Go to Settings > Cellular.
2. Tap Add Cellular Plan.
3. Use your iPhone to scan the QR code that your carrier provided - you may be asked to enter an activation code.

Or to activate with a carrier app:

1. Go to the App Store and download your carrier's app.
2. Use the app to purchase a cellular plan.

You should also label your plans in Settings > Cellular. Tap the number whose label you want to change. Then tap Cellular Plan Label and select a new label or enter a custom label.