T-Mobile is expanding its support for eSIM technology today, offering the digital SIM card technology for its post-paid plans, in addition to the prepaid options that it’s supported since last December.

Unlike the prepaid options, though, which can be purchased and configured through an app, converting a post-paid SIM to an eSIM requires visiting a T-Mobile store or contacting T-Mobile customer support. Once you’ve gotten your account set up with an active eSIM, you can download it to a new device by following the instructions on T-Mobile’s support document here.

Just iPhones for now

As to why a T-Mobile customer might want to do this? Moving your main, post-paid plan to an eSIM means that you can simultaneously use a second cellular plan off of a physical SIM card. That means that you could, for example, buy a second, local SIM to access data while traveling, or use your work and home phone number from a single device. The downside? You’ll lose the flexibility of quickly and easily changing devices, one of the best benefits of standardized universal SIM card technology.

So far, only the iPhone XS, XS Max, and XR work with T-Mobile’s eSIM setup, although presumably Apple’s upcoming iPhone 11 lineup will support it, too. But that’s still a pretty limited list of devices. As with all of Apple’s eSIM setups, there are also some restrictions: you can use both active numbers for voice calls and texting, but only one data network at a time.