T-Mobile has announced expanded support for the eSIM, which is a feature in the iPhone XS, iPhone XS Max, and iPhone XR.
The carrier previously introduced eSIM support for prepaid plans, but starting today, the eSIM can also be used to activate one of T-Mobile's postpaid plans.
With the new eSIM support, customers who already have a phone plan with one carrier, like AT&T or Verizon, can sign up for a standard postpaid plan with T-Mobile and use services from both carriers simultaneously on a single device.
Combined with the physical nano-SIM slot, the extra eSIM option is useful for iPhone owners who need to access both work and personal numbers on one device, or set up a device with an international number while traveling.
The eSIM can also be used to activate an iPhone with T-Mobile without the need for a physical SIM card.
T-Mobile says that customers interested in activating their iPhones with a postpaid plan via eSIM can visit a T-Mobile store as of today.
Along with T-Mobile, Verizon and AT&T offer eSIM support in the United States, but Sprint does not.
Source: https://www.macrumors.com/2019/08/28/tmobile-postpaid-esim-support/
