If the report is true, prepaid customers will be able to make use of the eSIM feature through the upcoming T-Mobile app. it is unknown if the alleged app will also be available to post-paid account holders.
"According to PCMag, T-Mobile plans on doing eSIM slightly differently than AT&T or Verizon, at least for its prepaid customers. According to the report, T-Mobile will be offering an app-based solution, allowing users to add a prepaid line easily and effortlessly add to their iPhones with eSIM technology."
https://9to5mac.com/2018/12/06/t-mobile-esim-app/
"According to PCMag, T-Mobile plans on doing eSIM slightly differently than AT&T or Verizon, at least for its prepaid customers. According to the report, T-Mobile will be offering an app-based solution, allowing users to add a prepaid line easily and effortlessly add to their iPhones with eSIM technology."
https://9to5mac.com/2018/12/06/t-mobile-esim-app/