Sometimes NSA analysts need to make "cover" phone calls, without leaking the fact that they're being made from the NSA. In 2005, the NSA owned 40,000 telephone numbers from area codes that were publicly connected to the agency. But for situations in which an analyst needs to make a public phone call without leaking their NSA affiliation, the Special Operations Support office has some options: "Anonymous telephones" are lines that physically connect to the NSA, but they are registered to "DoD," and only "examination of vendor-billing records will disclose affiliation with a physical NSA location." "Cover telephones" are registered using alias names and P.O. boxes, and do a more thorough job at hiding NSA affiliation.