Previously, T-Mobile customers could only upgrade by going into an Apple Store. But now you can enroll in the program in the Apple Store app. T-Mobile joins other carriers to the program, including Verizon, Sprint, and AT&T.
The program includes AppleCare+, which gives you coverage for two accidental damages a year—for two years—and costs US$99 per incident for iPhone X users. Phones are also unlocked, which gives you the freedom to switch carriers.