I think that by "dossiers" this guy meant "social network information from communication logs". They can start with your number (any number) and see who communicates with it. And then see who communicates with those people, and so on until they find a link to a terrorist or whatever.
If you're doing something that the government doesn't want you to do, use a burner phone. And drive 30 minutes from your home, and use a proxy server to connect to the internet. Any federal agent can get a record of every call you make with a boilerplate warrant. The NSA can dig up the full text of all of your conversations with a tech support ticket. Welcome to 2012.
If it makes you feel any better, facebook has a similar level of information about you and they haven't done much harm with it.