"Back in the day," as my teenagers would say (or during "yesteryear" or "yore," per Rachel), not only were the telephones mounted on (and permanently attached by a cord to) the wall, but because every line was a "party line" (which is what they called it when you shared a phone line with your neighbors and all they had to do is pick up their phone to listen in on your conversations), the walls definitely had ears!
I can remember my mother putting her hand over the mouthpiece of the phone (not one quite this ancient, it was the 1960s, but still a wall phone in the kitchen) and saying to my dad, "I know that nosy Mrs. Rosenberg is listening in!" Sometimes my dad would be talking to someone and then stop and say "I can hear you breathing! Hang up! I'm not done yet!" and there would be a gentle but audible "click."
It wasn't long before the party line became a thing of the past, but while it lasted you were sometimes more involved with your neighbors than you wanted to be. I guess calling it a "party line" made it seem more festive than "snoop heaven" or "no privacy for you."
I drew this with an 0.3 LePen, and then watercolored. This one's for you, Kirst.