Being a reporter, I make dozens of phone calls every week. I call people up and try to state my business clearly and quickly. Only very rarely do people hang up because they think I'm trying to sell them something.
But quite often -- including many times when I've called government offices -- once I introduce myself, the person at the other end of the line responds by saying, "Okay." Like this:
Me: "Hello, my name is Alan Greenblatt and I'm a reporter with Governing Magazine."
Them: "Okay."
What's so annoying about this is how dismissive they invariably make the word "okay" sound.
The way they say "okay" makes it sound like, "What the heck do you want?"
And also like you're distracting them from about 5 million more positive experiences they might be having other than talking to you.
It might be asking too much for them to respond, instead, by saying, just for example, "How may I help you?"
But people answering phones in a professional environment should be able to sound professional and even welcoming, rather than curt and put off.