Some people hate dealing with voicemail. Actually, I typically don't mind. It's an effective way to communicate. You can call someone, tell them what you want, they can call you back, tell you the answer - effective communication.
So what happens when someone calls and leaves a message like this - "Hi this is John, I need to talk to you, call me." Then you call him, he's not in - "Hi, this is Randy, returning your call, call me back."
Then you get on the phone, John calls back, blah, blah, blah.
So, instead of getting on the phone, you wait on John to call back. And wait. And wait. How long is the appropriate time to wait?
Wouldn't it be better if John left a message instead?
(You might guess, this was a frustrating day).