Right now I work in a call center and I have roughly an 8-hour shift from Monday to Friday. Communication is a completely different beast when you only have voice and conversational cues to communicate information.
Tone of voice, volume, word choice, interruptions or not, pauses (their length and after what words), speed of talking, and other voice cues indicate the relationship between the caller and the agent. My voice is hoarse and my singing voice is non-existent at the end of a day's shift.
Tone of voice can be condescending, encouraging, communicate boredom or interest. If there is a sing-songy voice, that can be condescending to someone who feels like they don't need additional help. However, a sing-songy voice can be helpful for older people who struggle a little more with technical navigation of the internet.
Volume of voice can indicate how we feel in regards to the topic, or even how we feel about the other person. It's interesting how having your voice sustained at a high level, to help them hear you, and actually feel a little angry by the end of the call. Like you were yelling. Which you were a little bit, but only because the phone connection was sketchy or they have difficulty of hearing. If you're quiet, empathetic people will try to simulate that calmer volume. If someone is bent on taking control of the call, they will try to amplify their voice to indicate authority. Interesting: calmer people always seem to feel better by the end of the call.
Word choice is very important for conveying how you personally feel about the situation and how they will interpret the situation. If I say I will "check the technical database" as opposed to "look for the answer online" then people will feel more comfortable with my ability to resolve their issue. Instead of saying "here's the number for what just happened" we say "here is the order confirmation, which functions as a receipt for the transaction". Word choice is critical in conveying aptitude and ability, especially in unfavorable situations.
Interruptions, or lack thereof, can be irritating or comforting. If someone is on a rant of issues, and starts repeating themselves, it's usually a flag that they have finished conveying their issues. If you calmly and politely interrupt to paraphrase and suggest a simple solution to start, that can be very comforting. If someone is trying to convey their problems and they are interrupted to ask for follow-up details before they have finished conveying the issue, that would be irritating. It could make them feel like they are not being heard, or that their opinions are not being respected.
Pauses can be used as moments to communicate a repeat of information already given, or to allow a moment for someone to process an idea. If I tell someone how to fix something, they repeat the same problem, I remind them how to fix something, and they repeat the same problem. I leave a tiny pause before offering a slightly-modified solution. That pause is there to give them an opportunity to process the information and to realize that I'm aware of the conversation going in circles. Pauses can be useful when giving instructions, and pausing after each completed step. This allows people to feel calm and successful in checking off steps to accomplish.
Speed of talking should generally match the urgency of the other person, as an empathetic decision. If someone is highly frustrated with something, speaking in a slow, quiet voice is most likely going to be offensive. If someone is high-energy, it is best to speak quickly and clearly with a lot of information that has been watered down. This will show that we recognize its importance for them, and it will enable us to be effective in addressing their needs in a way that will be satisfying and efficient for them.
Other verbal cues like "mmhmm" can express understanding and encouragement to continue, if placed during pauses. If the "mmhmm" interrupts the person, it can send the message that we understand and don't need to hear more about it. Careful about how you're using those "mmhmms".
These are some general observations. Human beings are so interesting.
