I have never used a computer to call from - namely because I have never had scripts already computerised and dont usually have the time to type it up and experiment, but I am thinking about it for my next show.
I cary my laptop with me everywhere anyway, it is more a matter of actually working out my own system - I have all the programs, I have just not made my own method yet.
The way things are these days, I carry arround half an office with me. At uni, when I am sming a show there, I can be walking arround campus and an actor will approach me and start talking show - out with the prompt copy, note book and a pen. Then I leave to go and do some pro work. Walk in the door "I did not get a copy of xxxxx" or "I left notes yyyy at home" out with the laptop, into the car to grab the printer. Print it off. I need a cart that follows me arround with my laptop, all of my prompt books, note pads, paper, pens, pencils, staplers the lot... or a personal assistant to carry them all for me. Then there are the times when I am shopping and I run into the local amdram 'star' or director. My trolley turns into a virtual office.... grr. I wish, just once, that people listened to me when I say at the start of rehearsal period "I make myself available half an hour before first call, until half an hour after the last call, and any gaps in between, feel free to see me then. If that is not convienient, call me or email me and we will arrange a time that suits you". Serves me right for burning the candle at both ends and the middle. I suppose that is why I am loath to have a computerised copy - it would waste even more time booting up the computer every time I am stopped by a member of one of my shows outside of hours (on average, 3 to 4 times a day)