It appears that T-Mobile too has given up on Windows Phone. According to a report from Windows Central, T-Mobile is set to retire its Windows Phone app come August 25th, pointing users of the app to the mobile website instead.
Word on the retirement is being delivered to users via an in-app message:
Thanks for being an awesome T-Mobile customer! We're always finding new ways to provide you with the best experience possible. Unfortunately, our Windows app will no longer be supported beginning 8/25/2017. Moving forward, you'll be able to manage your account at My.T-Mobile.com.
At first glance, this is a rather odd move given that T-Mobile recently updated the app with a completely new look and interface. The wireless network, though, did also recently abandon its last Windows Phone, the Alcatel Idol 4S, so it would appear that T-Mobile is now focusing more on iOS and Android devices.