The carrier said "simple software updates" make the feature possible, with a video call activated with the push of a button on the screen.
In a blog, T-Mobile Chief Technology Officer Neville Ray advertised T-Mobile's approach to video calling as being simpler than competing approaches.
"Of course there are apps that do video calling," he wrote. "But this isn't another app. T-Mobile Video Calling represents a high step forward...[it] works right out-of-the-box from your smartphone's dialer. There's no need to search out, download, configure and register additional apps."
Some video calling services have worked only with Wi-Fi or on slower cellular connections like 3G. In contrast, T-Mobile said, its Video Calling works on Wi-Fi as well as any available LTE 4G connection by using data from a customer's high-speed "bucket" of data. When a user moves off either LTE or Wi-Fi, the video switches over to a voice call.
By comparison, FaceTime video calling on the AppleiPhone only worked in Wi-Fi until the emergence of iOS 6 in 2013, when a user could use 3G or 4G cellular as well, after making changes to phone settings.
Ray said the two newest Android devices from Samsung will support T-Mobile Video calling right away, and the older Galaxy S6 and S6 Edge devices will do so starting next week. By year's end, he promised three more video calling devices, for a total of seven.