There's an ongoing criminal case in Sweden where a website streamed their porn movies for "free". However, in the fine print it said that in order to watch this you need to pay X. So basically the company could bill you just for watching.

This wouldn't be any problem since people are anonymous. The twist is that the company behind it actually had a deal with some of the phone network operators where they sent the phone number as a header for mobile devices.

The result was that hundreds of people got invoices and were told that their personal details would be exposed if they didn't pay.