As we travel around with our cell phones it's hard to imagine what it must have been like to receive only rare phone calls, and always connected by an operator. If you weren't home the phone would just ring and ring until the operator decided the person was not home. I'm not familiar with this kind of phone though. It appears that the speaker and receiver were fixed and you would just stand next to the phone and talk.
It looks like the girls who sent this, Marvel and Mable, pasted their photo over the printed message. They sent the card from Kingston, Missouri to Marnie Howard in Pueblo, Colorado. I couldn't find much on Marvel, Mable, and Marnie, except that Mable was born in 1900, and her father John was a mail carrier.
Here's the back of the card, with a message that says:
Hello Marnie
Goodby.
Marvel P.