🚀 go-pugleaf

Many of the tones at the beginning of recorded announcements were originally
put there for a product that the FCC did not let the Bell System
put into service - namely Voice Storage System.  It had an answering
capability, similar to answering machines, plus the more interesting
voice mail capability that allowed you to send a voice message at
a particular time.  It recognized the tones generated in announcements,
so that it would not deliver a message to an announcement.  The tones
are MF (Multi-Frequency, the type of signal that blue boxes used).
MF signals were designed for ease of generation and detection, as
Touchtone was designed for ease of listening.

John Haller