Kraftwerk, from Wikipedia:

"The band is notoriously reclusive, so much so that it is rumored that their label partner, EMI does not have its phone numbers. Another notable example of their eccentric behavior was reported to Johnny Marr of The Smiths by Karl Bartos, who explained that anyone trying to contact the band for collaboration would be told the studio telephone did not have a ringer, since during recording the band did not like to hear any kind of noise pollution. Instead, callers were instructed to phone the studio at a certain time on the dot, whereupon the phone would be answered by Ralf Hütter, despite himself never hearing the phone ring."

“The telephone is an antiquity—you never know who is calling, there is no image, it is an outmoded product [that] constantly disrupts work.” — Ralf Hütter ^[6]