Apple's eSIM technology allows for dual-SIM-like functionality using two lines at once, and it is in the iOS 12.1 settings now, as first spotted by 9to5Mac. But activating the eSIM still requires carrier support to become functional.
iOS 12.1 beta users can find the eSIM sign-up screens in Settings > Cellular, which has details of their first line linked to their physical, removable nanoSIM that's slotted into their iPhone. If they wanted to add another line to be assigned to their eSIM, they’d click on “Add Cellular Plan,” as Apple describes on its Dual SIM website guide.
That brings them to a screen where they can scan a QR code provided by their carrier, or they can click “Enter Details Manually” at the bottom of the screen. Even though users can get this far in the iOS 12.1 beta, without carrier support, they can’t really use this feature.
Carriers will support dual lines...eventually
At the event introducing the new smartphones, Apple noted that three big US carriers (AT&T, Verizon and T-Mobile) had already signed on to support dual lines, as well as non-US carriers like Vodafone, Bell and Deutsche Telekom.
None have revealed when users can add a line on their eSIM, though it will likely be after the iOS 12.1 update is officially released. That launch date may come next month alongside the iPhone XR launch on October 26.
We know even less about how the iPhone XS that Apple is producing exclusively for China, which will have two physical ports for nano SIM cards, will be supported by local carriers. As far as we know, that version won’t be available elsewhere.