Malte Spitz, a German politician, sued Deutsche Telekom to get 6 months of his own connection data, collected by the telecom company. Goal was to show what information could be gathered by connecting this data to publicly available information, like tweets and blog entries.

Image copyright: Zeit online

This profile reveals when Spitz walked down the street, when he took a train, when he was in an airplane. It shows where he was in the cities he visited. It shows when he worked and when he slept, when he could be reached by phone and when was unavailable. It shows when he preferred to talk on his phone and when he preferred to send a text message. It shows which beer gardens he liked to visit in his free time. All in all, it reveals an entire life.

Link.

See also:
Data Retention Directive
Telecommunications data retention