Earlier quoted context omitted.
That's why we have voicemail. If I'm not available leave me a message.
I could talk for hours about the times I've been legitimately unable to take a call and had people repeatedly call my desk/mobile phone and either (A) refuse to leave a voicemail, thinking calling back repeatedly for 20 minutes would work or (B) filled my voicemail to capacity with multiple messages throughout the day. Hours.
Seriously, it's highly productive. At least it was for me.. It's their interest to reach you, that's why they are calling you and not the other way around.