I hate calling people because I'm always worried that I'm interupting something important or otherwise harassing them at a bad time. Yes, I realize they could just tell me they're busy and hang up, but I know that if I get a call from someone I'm always too polite to get them off the phone unless I really urgently can't talk. I'm always worried that if I call someone and they claim to be not busy they are still, secretly, annoyed at the call and too polite to say anything.
I hate receiving calls because I don't have adequate time to prepare myself. I'm minding my own business, playing a video game, reading, watching television, doing homework, when suddenly with a piercing shriek I am thrust head-long into an unanticipated conversation. I find myself at the wrong end of the element of surprise. This is why, when you first get me on the phone, I will tend to stammer a lot; I have been thrust out of bed into battlefield conditions and am still trying to get my wits about me.
This is why I don't own a cell phone. It's bad enough having a phone in my room. The idea of having a phone ready to strike at a moment's notice, at any time, day or night, wherever I might be, is utterly horrifying.
Given a choice, I would always, always prefer to transact business through some form of electronic text, be it e-mail for long, thought-out conversations or IM for faster coordinating-future-activities type communication. Talking on the phone is a barbaric relic of the Twentieth Century that we would do well to put behind us.