Gardner Fox, who wrote the Justice Society stories, made her the society’s secretary. In the summer of 1942, when all the male superheroes head off to war, Wonder Woman stays behind to answer the mail. “Good luck boys,” she calls out to them. “I wish I could be going with you!” Marston was furious.
I think that this passage relates to the unplugged telephone. While Wonder Woman is allowed into the Justice Society as a member, she is made the secretary and isn't allowed to head off to war along with the male superheroes. The idea that she is in the Justice Society would make people assume that she is using the powers and abilities she has just as any other superhero would (just like how if the wonder woman telephone is displayed, people would assume that it is useful and working just as any other telephone). However, she is not allowed to show her full potential because she is being suppressed, and instead is just in the Justice Society "for show" (just like how an unplugged phone doesn't allow it to be useful, but simply a display or decoration).