The United States has paid an American firm $8.4 million to maintain, for the next five years, the U.S. Army ground station that provides the hotline between the United States and Russia. This link was established in 1963, after the lack of such a quick connection almost led to nuclear war (over Russia placing nuclear armed ballistic missiles in Cuba.) Since then, the link has added additional tasks. These include the Nuclear Risk Reduction Center and the U.S. Space Command's Joint Data Exchange Center. The link provides instant communications between the American and Russian president, as well as between the U.S. Secretary of Defense and the Russian Defense Minister.
Three years ago, China and the United States agreed to establish a hot line between the Pentagon and the Chinese Defense Ministry. This would make it easier to defuse any accidental (or intentional) confrontations between U.S. and Chinese military forces. Such a hot line has been under discussion since early 2001, when a Chinese fighter collided with an American patrol aircraft off the Chinese coast.
The hotlines are tested frequently, at random times, in both directions, to insure that, if there is a need (and one arises every few years, even if every incident does not make it into the news), the thing will work.