We have retro rotary telephones, and I'd like to make a hold button for the one in my office in the UK. This is literally a "ye olde rotary phone" (1940s) made from bakelite
I have fairly basic electronics skills but I don't actually know how the phone works, in that sense anyway.
Is this just a case of switching out the circuit to one playing "The girl from Ipenema" or is it more complicated than that?
For example, what is it that keeps the line open if I make an outgoing call? Could I accidentally cut the call or does the line need to go open circuit to do that? What are the voltage limits?
(I would just buy one, but can't find any!)
[UPDATE]
Some good points have been made in the comments that bear highlighting.
When I used to work in a shop repairing computers (about 40 years ago) we also sold telephone handsets to the public; the ones with green stickers were allowed to be connected to the phone network, the ones without - or with red stickers - were not. I'm pretty sure the same or similar system exists today, especially with digital exchanges, "digital voice" etc.
So, to be clear, nobody should be connecting unauthorised equipment of any kind to the telephone network.
