Tone of communication refers to the way in which what one is saying comes across. I would argue that, in "Hills Like White Elephants," the woman's tone is imaginative and lighthearted, showcasing a sunny personality and free spirit. The man's tone is slightly argumentative, turning later to being persuasive. The difference in tone almost makes it feel like they are having two different conversations.

The woman's imaginative tone comes across early when she tells her companion that the hills in the distance look like white elephants. The man becomes defensive when his companion tells him that he wouldn't have seen a white elephant, demonstrating his touchy mood. The tone of communication here is a literary device used to mark the tension that exists between Jig and her partner at this moment in their lives.

From starting out giving laconic responses to Jig's musings about the world around them and their drinks, the man's tone becomes persuasive, attempting to convince Jig to abort her pregnancy by explaining how simple the procedure is. He becomes a far friendlier man as he explains the support that he will give her if she does what he wants her to do.

The tone of the two respective voices in this story shows their mindsets to be world's apart and showcases the breakdown in communication that has happened in their relationship—if indeed there was ever a time when Jig and her partner were able to communicate effectively.

Hemingway is quite skilled at developing a tone of communication between both main characters that displays an existence in different realms.  Both speak in what is almost dual monologue.  While they are physically together, it is evident through their tone of communication that they are emotionally distant.  This is evident from the first exchange between both characters:

'They look like white elephants,' she said.

'I've never seen one,' the man drank his beer.

'No, you wouldn't have.'

'I might have,' the man said. 'Just because you say I wouldn't have doesn't prove anything.'

The tone between both main characters is reflective of existing on opposing planes.  Neither one of them is able to merge with the other.  Each exists on their own level.  One says that the mountains seems to appear in a specific manner, the other brings it back to themselves, and the tonal dynamic is one necessarily one in direct conflict, but rather on different planes of existence. This is further seen when the woman says, "You started it...I was being amused. I was having a fine time" and is further enhanced when he says, "Well, let's try and have a fine time."  This is the tone that underscores the decision to have an abortion.  There is never a tonal quality that reflects full understanding of the implications on either side.  The tone of communication between the two reflects how each of them is unable to embrace the other with full immersion.  The ending shows this tone in full bloom:

'Do you feel better?' he asked.

'I feel fine,' she said. 'There's nothing wrong with me. I feel fine.' 

Hemingway has created a tone where there is communication, but its core is one of emptiness because of the dual planes in which each lives in reference to the other.  This disconnect is the foundation of their relationship, something that is illuminated in the communication tone that emerges between both of them.