AUTOVON brings back memories from the mid 1960s. I was on a US Navy Oiler which was getting some maintanance from the shipyard in Subic Bay, PI. The shipyard officer we were assigned hosted a small party at his home and learning that I had been frustrated in not been able to complete a phone call to my wife in California imitated a call for me from his phone. Amazingly the call went through almost instantly and as I heard my wife answer an operator said more or less: "Sir, are you aware that this priority is used by the Joint Chiefs of Staff and ... . Sir what is your name, rank, and position?" Operating under the conceit that I may be stupid but not that stupid I quickly hung up.
The handset was a 'regular' one, not the one illustrated.
And a reminder of how unsecure and unencrypted these communications channels were. That operator not only could listen in, but was certainly instructed to listen in on all such priority calls in order to police them. No encryption. No channel hopping. Anyone with a handset and a pair of alligator clips could have literally clipped into the line at any point. Anyone in the know would also be able to monitor a trunk line looking for that priority signal. So it would probably have been more secure to hide amongst the masses by not pushing the priority buttons.
The handset was a 'regular' one, not the one illustrated.