You know what really grinds my gears? When someone pages you and then walks away from the phone.
It annoys me to no end when I try to promptly return a page, only to be met with endless ringing on the other line. When you page someone, you have to give them a grace period to answer the page. We can argue how long that grace period should be, but at least sixty seconds.
Yesterday I was waiting all afternoon to get a callback from a surgeon's office on my pager. When I finally got the page, at like 4:30, I quickly ran to a phone to return the page. The person who paged me was on the phone. I hung up and called back, this time getting a message that they had left for the day.