'Exited' means they will no longer supply or support the T-Box. This doesn't mean it will stop working as a TV recording device for you. It was supplied to work with many other features as well as the free to air recording such as streaming content from Foxtel. When they no longer register the device all the other content you were able to get will cease and only the free to air will continue to work for you. Already from Telstra's perspective the T-Box is considered redundant and was replaced by 'Telstra TV' which while providing a wider range of product does not have free to air recording.
From Telstra's Critical Information Summary on the T-Box is this:
"When your T-Box is not registered or connected to a BigPond
Broadband service, features will be limited to free-to-air digital
channels, basic TV program guide (programs on now and next only)
and basic recording features such as manual timed recordings."