Apple released iOS 12.1 yesterday, adding support for a second SIM card to the iPhone XS and XR through the use of a digital eSIM. Apple may have technically added support for eSIM cards, but none of the major US carriers are ready for it. According to a report from MacRumors, AT&T, Verizon, and T-Mobile are all delaying their adoption of eSIM until later this year. (Sprint wasn’t included in Apple’s original announcement, but it told PCMag that it will support eSIM at some point.)
So if you’re a US cellular customer, you can’t actually use a second SIM with your phone unless you’re using one of the international carriers that do support eSIM.
According to MacRumors’ report, AT&T is delaying the implementation of eSIM for its customers due to issues with Visual Voicemail. Verizon had already announced its delay yesterday; the company is focusing on resolving issues where Verizon lines used as a secondary number in an iPhone dual-SIM setup would be stuck on 2G CDMA speeds before offering eSIM support. T-Mobile commented to PCMag that it’s also still working on its eSIM support, which will be available once its software is ready.
Apple’s website notes that all three of those carriers will offer eSIM support “later this year,” so hopefully these various technical issues will be resolved shortly. Since the iPhone can only offer dual-SIM support if one of those SIM cards is an eSIM, you can’t take advantage of the feature with US carriers until at least one of them gets things working.