If you're a fan of Pink Floyd's Young Lust (from the album "The Wall" released in 1979) but are scratching you head as to all the beeps and boops you hear during the telephone call portion of the song - this article explains it all.
And the sad thing about that central office is that it used to house a ton of equipment. And toll operators. Now it's a packet switch. Probably taking up the back corner of the first floor.
The buildings are called Central Offices. The switches inside are the actual pieces of equipment handling the calls. Yes, "telephone exchange" is also used, but not so much in the United States.