When Apple released the iOS 12.1 update back in October, it enabled dual SIM and eSIM support on the iPhone XS, iPhone XS Max, and iPhone XR. The major U.S. carriers were ready for the feature at that time, but it looks like that's now changing.

AT&T says that it's now activating eSIM for the iPhone XS, XS Max, and XR. Customers can visit a retail store to get a QR code and activate their eSIM, which will be supported on all prepaid and postpaid plans.

Meanwhile, Verizon has confirmed that it'll begin supporting eSIM on Apple's new iPhones tomorrow, December 7.

T-Mobile hasn't made any official eSIM support announcements, but images of the carrier's eSIM app have been shared by PCMag. They show that users will be able to activate a prepaid line on an eSIM using just the app. T-Mo is reportedly planning to deploy the app to its staff for training tomorrow and expects to launch it to the public by the end of 2019.

Sprint's eSIM plans are a bit more vague. The carrier told FierceWireless that it will support eSIM at some point in the future, but it has no timing info to share.

With eSIM, iPhone XS, XS Max, and XR users can use a SIM for their main line and then activate a second line on their phone without the need for a second physical SIM. This could be useful for someone who has personal and business phone numbers and doesn't want to carry two phones, or someone who has one carrier but would like to test another carrier without getting a second device. Dual SIM phones have long been popular internationally, and so it's nice to see them finally begin to gain traction in the U.S.