It looks like the data that was sold by a T-Mobile employee is out there! I got a call from someone asking about my T-Mobile contract and offering me a better one. It sounded like it was from India. On checking the number, 05603018128, it looks to be a virtual number used by a VOIP system. In otherwords, it is untracable. When I told them I was aware of the missing data, the caller hung up.

If you have received that call, I suggest comlaining to the following:
Information Commissioners Office – unfortunately they can’t do much unless you can identify them, but at least it will help if someone does.
T-Mobile– although they are not making the calls, it is worth telling them in case they are able to trace the data.

In the meantime, I have commented on the subject at Mobile Marketing Magazine.