Well some moded spike boxs/busy boxs/tap phreak devices keep the voltage up with a 9 volt. I was thought way back that lines were 9 volts, but their not. I don't know off the top of my head the correct volts/amperage but I'm sure it'll come to me...switches, and other devices have regulators. Also they have traps for high voltage, due...directly to instances like, and occuring from spikes/boxs. Aka surge supression, liek from lightning bolts, and PHEER:)
Digital lines normally have 50 volts I believe, and 190volts at a max amperage...I believe. But you have to be very specific on it. You used to be able to make a rotary phone on a mechanical connection ring by dialing yourself, and at about .5 seconds hanging up. Heh I know because I used to make my whole house ring to have fun. If you wanted to test your ringage, hookup a landline to a rj11 dual jack, and then a split rj11 line bare to your voltage expierement. Of
course I've never tried hooking up a rotary to a cabinet jack, then called a anac for the number, dial it, and hung up. While every line in the cab was looped. But...it could just cause every line on that cab to ring, and every person to pick up. Creating a "Hello" or "Can you Hear me Now", party line. But then some would say the voltage would drop to low if everyone picked up...well it's fairly well know that switches, and cabs have backup power(most).
Also they have a power limit. But the fact is, it's not been tested to my knowledge. Now the real question is on the first pickup would every line stop ringing, or what if one was ringing still while everyone was on? Would it create a busy tone? Of course each of these lines have a number, and they each go to a jack on a cab, that comes from a switch that redirects to that. What I wonder is what digital device today is used to keep track of all those redirects, or findings. Heh, the Technical aspect on telephony electronics is a changing amorphis so I'm not one to be up on everything, and no one knows everything. People just mostly know parts. If not they wouldn't learn once in a while. Or all the time.
My mind is a little distanct, since I'm multitasking, but I hope that helps, and that I'm close enough from memory.
"Beware the Jabberwock, my son!
The jaws that bite, the claws that catch!
Beware the Jubjub bird, and shun
The frumious Bandersnatch!"