T-Mobile in Germany, like most carriers, do not offer visual voice mail on Windows Phone, despite the feature being built into the OS and usually provided for the iPhone.
Some angry Windows Phone complained on their forums about paying for a service the carrier was not delivering, and after initially saying in November last year that the service will not be available, they have returned last week and confirmed the carrier was working at providing Visual Voicemail to their Windows Phone 8 customers.
Of note however is that the support staff has not said they are working on Data Sense, the other half of the question. Â The feature is unfortunately carrier dependent, meaning things as simply as finding the nearest WIFI hotspot is still dependent on carriers signing up for the service.
See the thread at T-Mobile Germany here.