Let alone back in the day landline phones were used as wiretapping devices, even when you are not speaking on the phone and it's on hook. The telephony standard

Let alone back in the day landline phones were used as wiretapping devices, even when you are not speaking on the phone and it's on hook. The telephony standard was designed with this in mind, i.e. the possibility to turn any phone on-hook or off-hook to a listening device.