See this for how soldiers called home from Vietnam. http://afvn-radio-tv.org/MARS_in_Vietnam_2.html
A soldier made a call to a short wave radio operator in Vietnam who transferred it to another operator in the US who then transferred it by a collect telephone call to the soldiers home. It was like talking on a radio, you had to say "OVER" at the end of each sentence before the other party responder and said "OVER" again. All the while two radio operators monitored the call. The charge was for a collect telephone call from the location of the US radio operator to the soldiers home. Calls were limited from 3-5 minutes, and normally made late at night in Vietnam.
Vietnan telephone calls
A soldier made a call to a short wave radio operator in Vietnam who transferred it to another operator in the US who then transferred it by a collect telephone call to the soldiers home. It was like talking on a radio, you had to say "OVER" at the end of each sentence before the other party responder and said "OVER" again. All the while two radio operators monitored the call. The charge was for a collect telephone call from the location of the US radio operator to the soldiers home. Calls were limited from 3-5 minutes, and normally made late at night in Vietnam.