For a long time it was nearly impossible to tell who owned a cell phone because it didn’t provide a name on the caller ID.
Recently tnid.us has came to the attention of the security community and is giving out that information for free. I am not exactly sure how they do it but out of 10 numbers I checked 9 gave me the real name of the owner and one gave me “wireless customer”.
Good news is that there is a way to get off their list. They have a delete option that I would recommend you use if you value what little privacy your cell phone number carries.