Fascinating, thanks for that.
A lesser known fact about ring tones is that even today, for wired networks, they are almost invariably generated by the remote (called) exchange. The reason for that is, there needs to be an instantaneous transition from 'ring tone' to speech when the called party answers. If the called exchange had to signal back through all the intermediates, and tell the caller's exchange to stop ring-tone there might be a signalling delay, and so "Hello" might be truncated to "lo", or even just "".
I therefor find it comforting to think, should I ever be connected to an exchange that time has forgotten and retains early 20th century technology, I may actually hear one of these tones again.
Doesn't apply to calling mobiles, where ring tone is usually locally generated, they don't want to waste precious airtime on tones. That's why, when calling a mobile, you often do hear just "lo" or even "".