Apple’s new Dual SIM Dual Standby feature is a game-changer — but there’s a catch.

When Apple announced the new iPhone XS, XS Max, and XR on Sept. 12, one particular feature captured the imagination of international travelers and multiple phone-owners alike: the dual SIM.

Josh Miller/CNET

If the processor is your phone’s brain, the SIM, or subscriber identity module, is its soul — a tiny, little chip that stores your phone number and connects you to a cellular network. Essentially, it’s what makes your phone your phone.

If you’ve ever wanted two phone lines on one device, Apple’s new Dual SIM Dual Standby technology could be a life-changer. It will make it much more practical to have two phone numbers on one phone — one for business, another for personal use. And it will make it considerably easier and less expensive to use your own phone when traveling abroad.

iPhones have always had one “plastic” SIM card — until now.


Though the beta release of iOS 12.1 includes a crucial component of the technology — eSIM remote provisioning — Apple won’t deliver it to the general population until later this fall. Of course, it won’t be the primary factor for the vast majority of people shelling out for a new iPhone ($999 at Sprint) in 2018, but the debut of the iPhone XSiPhone XS Max and iPhone XR marks a new era of dual-SIM phones going mainstream.

We don’t yet know all of the details about how, when and where Apple’s dual-SIM feature will work. But based on our current understanding of how the technology will be implemented, there are some limitations. For now, here’s what we know about Apple’s dual-SIM — and what it means for the three new iPhones.

Note: The information presented below is everything as we know it now. If you’re buying an iPhone XS, XS Max or XR to take advantage of dual-SIM/eSIM technology, make sure you buy an unlocked phone (see below) check with your provider(s) first before committing to a purchase.

What does Apple’s dual-SIM announcement mean?

The 2018 iPhones will let you have have two different phone numbers on the same phone. You’ll be able to make and receive calls and send and receive texts on either line.

Why would I want a dual-SIM phone?

There are two major benefits. You can have two different phone lines — say, one for business and another for personal use — without the burden of carrying two phones. And when traveling internationally, dual SIM makes it easier to add a local plan to your phone to avoid costly international roaming and data charges.

So, the iPhones will have both an eSIM and a plastic SIM?

Yes. The new iPhones will have a traditional plastic SIM, the familiar hardware-based SIM chip that identifies you to your carrier network, and an eSIM, the newer software-based equivalent.

And here’s the big thing: the eSIM can accommodate multiple phone numbers — which you can add, delete and configure right from your iPhone’s settings. In contrast, a plastic SIM needs to be physically removed and substituted.

In theory, once eSIM technology is widely supported by carriers in the US and internationally, Apple could phase out the plastic SIM entirely. For now, in giving the 2018 iPhones both a plastic SIM and eSIM, Apple is covering all of the bases.

What is Dual SIM Dual Standby?

Apple’s take of dual SIM is called Dual SIM Dual Standby. It means that the new iPhones can manage two phone lines simultaneously — calls coming in to either line will ring your phone, and you’ll be able to easily make calls and send texts from either line without reconfiguring settings or swapping out SIM cards.

Note that you won’t be able to send and receive data on both lines simultaneously, however; if one line is on a call, incoming calls to the other number will go to voicemail.

How is eSIM different from Apple SIM?

Originally known as Apple SIM, the first version of Apple’s software-based SIM showed up on the LTE-enabled iPad and Apple Watch Series 3. Analysts believe that the fundamental technology is the same, but that iOS 12 may introduce improvements to the user interface.

Can I add lines from different carriers?

Yes. Apple says that you can add lines from two different carriers — if your iPhone is unlocked. And this is the major catch. If your phone is not unlocked, both plans must be from the same carrier. And, if a CDMA carrier — such as VerizonSprint, US Cellular, Boost and Virgin — provides your first SIM, your second SIM won’t support CDMA.


Can I use eSIM on a locked iPhone?

When you buy an iPhone directly from Apple, online or at an Apple store, it’s unlocked — meaning that it can be configured for and activated on any carrier’s network (e.g. AT&T, Verizon, Sprint). A Genius inserts an AT&T SIM, for example, activates your phone on AT&T’s network, and you’re off to the races.

But once a phone is locked, your options become much more limited. As my colleague Maggie Reardon explains, “a locked phone has a software code on it that prevents you from using it on another network. An unlocked phone either doesn’t have the software lock on it or someone was able to get a code that unlocks the software. Once a device is unlocked, you can pop out the SIM card and put in a different SIM and get service.” Most carriers require you to fully pay of your phone before they’ll unlock it, and other restrictions may apply. (AT&T’s Unlock Portal provides a checklist of requirements for unlocking your phone and switching to another carrier.)

An unlocked phone with a plastic SIM needs a new plastic SIM in order to switch to a new carrier. An eSIM, on the other hand, can accommodate multiple SIM profiles from multiple carriers. Until now, eSIM hasn’t garnered much support from carriers, who are understandably wary of making it easier for customers to activate another carrier’s service.

When will Apple launch its eSIM feature?

Apple will activate eSIM functionality in the iOS 12.1 update, currently in beta. US carriers will need to furnish a QR code before a line can be activated using the eSIM — which is likely to coincide with the public release of iOS 12.1. According to German site (as reported by MacRumors), some Deutsche Telekom users have reportedly already used eSIM to add a second line to an iPhone.


How do I setup eSIM on the new iPhone?

Owners of a 2018 iPhone will be able to access the eSIM through the iPhone settings. According to Apple VP Phil Schiller, you’ll be able to use the phone’s camera to scan a carrier QR code, which will kickstart the process for activating a second line. Then, iOS will let you select a default line for calling and messaging, choose a label for each line, and so on.

Apple has listed step-by-step instructions for setting up eSIM on its support site.

Can an eSIM be overwritten?

An eSIM can be overwritten and accommodate a phone plan from any carrier that supports the technology.

Which carriers support eSIM technology?

Apple says that eSIM works in 16 countries; in the US, AT&T, T-Mobile and Verizon currently support the technology. (A Sprint spokesperson assured CNET that the company will support feature in the near future.) Internationally, participating carriers currently include Truphone, Bell, EE, GigSky, Vodafone, Jio, Airtel and Deutsche Telekom.

At the Sept. 12 keynote, Apple VP Phil Schiller said that more carriers would add support throughout the fall and into next year.

Kent German/CNET

Are there are other phones that have dual-SIM technology? And doesn’t Google’s Pixel 2 have an eSIM?

There are plenty of phones that can accommodate two SIM cards, though most of them aren’t available in the US, but only a few so far that support eSIM. The Google Pixel 2 has an eSIM — but it’s primarily for use with Google’s Project Ficellular service.

Do I have to get approval from my main carrier to add a second phone number?

No, you don’t need approval or permission to add a second phone number. In fact, the major upside of eSIM is that you don’t even need to go to a store to activate that second line — it can all be done remotely.

Why doesn’t eSIM work in China?

Apple announced a special edition of the new iPhones for China, which will have two plastic SIM card slots instead of eSIM technology. According to Neil Shah, who covers mobile technology for Counterpoint Research, dual-SIM technology is popular in China — but very few carriers there have built out support for eSIM technology.

Dual sim iPhone  apple-event-091218
James Martin/CNET

Will we see more eSIM phones in the US?

Probably. After all, Apple often sets the trends. Will Stofega, who covers mobile phones for IDC, says that carriers have been wary of eSIM, fearing that it could lead customers to jump from plan to plan. But he points out that a new international standardset in June 2016 may pave the way for greater adoption of eSIM in the US and abroad, especially if carriers realize all of the benefits of selling and provisioning phones remotely — activities that have needed to be done manually in stores, until now.


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