Just stumbled upon this ear-pleasing (there’s an audio-sample on the webpage) performance from 1999: Improvisation for Two Altered Telephones.
An AM/FM radio circuit was added to the phone interface. “The radio circuit produces sound when its speaker output is fed back into the circuit at various points and in varying degrees. The resulting sound is controlled through the phone keypad and a few added knobs (variable resisters). The mouthpiece is also soldered into the circuit and the vocalizations (or air pressure) become amplified and filtered by the radio circuit.”
Performance by Julie Adler and Andrew Bucksbarg.
I hope Mister Roope will get some inspiration from it.