Former support tech here. Phone calls are not getting things done. Phone calls are usually telling someone else to do something. Information passed on phone calls is mostly lost as soon as the other side hangs up. I've had many 30-45 minute time wasters with clients when they called instead of thinking about what thy were trying to say and replying to their ticket. The phone kills the productivity of two or more people at once, so it's as bad as a meeting. Stop calling people and start finishing stuff.
Not exactly sure where I got this from, but I once read: "Call me - it's simpler" translates to you wanting to do your thinking inside my ear instead of your head.
That being said, from my own experience, the only thing that phone calls get done like no other medium (apart from a direct conversation, of course) is build interpersonal trust. It can further be a good way to diffuse tension right away because instead of having a customer write pages of mounting tension, they get a reaction immediately and that alone is usually enough to make the first steps towards reconciliation.
I've found that phone calls are good when people ignore or are bad at reading email (miss questions, fail to respond/read, don't read it completely, etc). For people who are good at email, phone calls are good (or the same as IM) when you need an in-depth back and forth conversation, for example, discussing some software bug.
