Lumia Black update finally hits T-Mobile Lumia 521
Now, the device can take advantage of some of the new features that come with the update.The update brings improvements to Bluetooth connectivity, and the ability to close applications with the upgraded “app switcher.”
Driving mode has also been added and there have been accessibility improvements made for those that are visually impaired. You will also be able to manage screen lock orientation with the update, bringing the Lumia 521 up to near feature parity with its bigger cousins. The update has just started rolling out so if you have not seen a notification about the update, try checking manually by going into settings, then phone update.
sources: T-Mobile via WPCentral