The Windows Phone 8.1 news just keeps coming today, and not to be lost in the shuffle are T-Mobile's rough upgrade plans for its Windows Phones. Both the Lumia 925 and lower-end Lumia 521 on T-Mobile will be making the jump to Windows Phone 8.1, and even 521 owners on the prepaid side with MetroPCS will be getting the update.
At this time there's no indication that the updates will be anything less than complete, with Cortana, notification center and an overall tightening of the screws throughout the OS. T-Mobile isn't giving any indication of an exact rollout date other than "this summer" (just like the Lumia 635 launch), but that's to be expected on day one.
Sprint has also announced its Windows Phone 8.1 updates to be hitting in the same time frame.