RE: old modem
Back in the '90's my employer would be hounded by assholes trying their copier supplies scam.
I had a dial up modem attached to the pc, and wired in parallel with the 'guts' of a 1A deskset1.
One day this asshole calls up, and tries to pull his shit over on me, and I wasn't having it. I fired up the modem program and had it dial a number. As the modem started to bang out the tones, I screamed out at the top of my lungs: "God dammit Sarah, you stupid c--t! Can't you see that I am using this line!" I then hung up on the SOB.
The boss walked in, and had this puzzled look on his face, a short explanation resulted in a smirk as he walked out of my office.
1 For those who are too young to know, the 1A key systems were electro-mechanical in nature, using a 'fat' telephone cable (25 or 50 pairs), and one or two rows of line selectors ('keys')
If you want further reading:
https://en.wikipedia.org/wiki/1A2_Key_System