The carrier continues its torrid pace of subscriber growth amid stiff competition in the wireless business.
iPhone and iOS news
The company also adds Apple Music to its program that lets you stream music without counting against your data plan.
Reports of crashes and reboots have popped up on various online forums, seemingly specific to T-Mobile iPhones. But so far there's no official word on the cause of the problem.
Some new software tucked into iOS 9 beta will let T-iPhones play with Apple's Continuity feature over T-Mobile's cellular network, not just over Wi-Fi.
The upgrade brings text messaging nearly on par with the features found in third-party instant messaging apps like WhatsApp and iMessage.
You'll also be able to call Canadian and Mexican numbers from the US at no extra charge. It's the latest in a series of programs as T-Mobile jockeys for better position.
But as one hand gives, the other takes away: The 10-gigabyte offering kills off an existing unlimited-data option at the same price.
In an interview, T-Mobile's chief operating officer spills the beans on a potentially attractive, alternative service plan and on its new cross-border program.
But there's a catch: You have to commit to a new smartphone as part of the new upgrade program. Also, only a select number of flagship phones are available for an upgrade.
The two companies are both looking to slice off a bigger chunk of the workplace. Will business users bite?