This BBC story explores the history of packet-switching:
. . . The problem with human speech is that most of it is made up of silence – be that the pauses between words, time taken to breathe or gaps when one person waits for another to speak.
Using most of a telephone network to transmit silence is not a very efficient use of that resource. Far better would be to find a way to fill the blank spots with the moments from others calls when those folk were speaking. . . . .