NYNEX was charging $1.95 per month in 1994; in 1976 the same service was 93 cents monthly. Silent numbers are often
plant test numbers that link to specific tests or control apparatus for network maintenance staff such as
ringback and
automatic number announcement circuit and are generally not for public use. In Norway,(and some other countries), the directory services in the 1970s distinguished between
secret number,
unlisted number and listed number with a
hidden address. The first type
secret number was typically used by celebrities (in this case the address was hidden as well). The second type
unlisted number was not listed in the (paper based) phone book, but was listed on the directory service (a voice call to 018 in the 1970s).
Listed number with a hidden address is useful for
women's shelter etc., where the number needs to be listed, but where the address is to be hidden from the general public. Naturally, there are many changes when directory services became available on the Internet, but this case shows that separate user groups may have different needs to hide various parameters relating to privacy. These unlisted numbers are made known to call recipients who have
caller ID, and are captured and recorded when used to call toll-free numbers. ==References==