Actually, at the beginning of the Cuban Missile Crisis there was no back-channel access between the U.S. and the U.S.S.R.  Finally in frustration Attorney General Robert Kennedy hand delivered a diplomatic note addressed to Nikita Khrushchev in a meeting with the Soviet ambassador Anatoly Dobrynin. The 'hot line' was installed between the two countries after the crisis was resolved and is featured in the Peter Sellers movie Dr. Strangelove.