One of the biggest advances in the new iPhone X S X S Max, and X R is the dual-SIM feature which allows you to use two mobile networks at the same time. Like Sinatra, Apple is known for doing things in its own way, so their dual-SIM setup is a bit different than you might think.
All three 2018 iPhone models are dual SIM, just not in the way most of us imagined. Traditionally, dual-SIM smartphones literally had two SIM card slots to allow the use of two networks. However, Apple went a different way and developed flagship to use only a Nano-SIM card and matched it with embedded SIM, eSIM short, together. That said, Chinese variants of the latest iPhones are using the traditional double-nano-SIM slots that give customers the ability to activate two lines more easily. For the rest of the world, creating a second line through eSIM is only possible in iOS 1
What is an eSIM?
Embedded SIMs, sometimes referred to as electronic SIMs, are not new to the mobile phone world. Android devices such as the Google Pixel 2 and the Nuu Mobile X5 use the technology as a viable alternative to physical Nano-SIMs to store your phone number and user data associated with the cellular network. Apple has even used eSIMs in select devices like the Apple Watch 3 and the iPad Pro.
The eSIM is a non-removable chip that is integrated with the new iPhones. If you enable this chip, it works the same way as a physical SIM, for which the new iPhones also have a slot (hence the dual-SIM aspect – a removable and an embedded one). As an added bonus, you can store multiple eSIMs in your iPhone, although you can only use them individually. At this point we are still unsure how many lines you can program into the eSIM of an iPhone. If we know more about it, of course we will review it again.
Because eSIMs are embedded in the hardware of your iPhone in the form of a microchip, compared to a physical Nano SIM card, eSIMs leave significantly less space on your device's motherboard and all its associated hardware components. This reduces the overall cost that may play a role in why the iPhone X R starts at around $ 950 in China, compared to $ 750.
You may feel a little uncomfortable using an eSIM to save your line as it is a way of tying you to your net and switching to one other companies to complicate better service. However, this is not the case, as the transfer of your line from one carrier to another via the eSIM of your iPhone is as easy as changing W-Fi networks.
In fact, the technology behind eSIM is so disruptive that big carriers like it. AT & T and Verizon have been contacted by the US Department of Justice, which will launch an investigation in early 2018 to determine if companies are working with the GSMA to prevent eSIM development and adoption. The investigation revolves around her alleged attempt to influence mobile technology to prevent innovation and maintain dominance.
Which carriers support eSIMs in iPhones?
Due to the general lack of infrastructure to support the iPhone's dual-SIM functionality via eSIM, only a handful of large carriers from ten countries offer eSIM support as of the release date of iOS 12.1:
T, T-Mobile and Verizon dual-SIM functionality with iOS 12.1, while Sprint has also said that they will support eSIM immediately or very soon. According to PCMag, Verizon will offer all regular plans for the eSIM, while T-Mobile and AT & T will offer eSIM support on a roll-out basis.
To repeat, variants of the iPhone X S X S Max, and iPhone X R with The standard dual Nano-SIM configuration is only available in China, Hong Kong and Macau.  Enabling a Line on an eSIM
As mentioned earlier, the ability to enable a line with an eSIM, primary or secondary, is only available in iOS 12.1 or later. Because of this, you probably already set up your iPhone using the traditional Nano SIM method and set the Nano SIM card number as the primary line.
However, make a secondary line with the eSIM of your iPhone easily enough. Keep in mind that your iPhone needs to be SIM unlocked if you want to use it with two different carriers. Otherwise, you must activate a second line with the same carrier. You can only use GSM plans if your iPhone is already on a GSM carrier or a CDMA carrier. You can not add a secondary CDMA plan if your current plan is CDMA-based.
However, you should also be able to transfer your primary line from your Nano SIM and reprogram it into your iPhone's eSIM to unlock the SIM card slot after you activate the phone. This allows you to use the physical SIM card slot when traveling or switching to a network that does not support eSIMs. Note that if you move a line from a physical SIM card to an eSIM card, the old physical SIM card is likely to stop working.