While it isn't micro-payments as many think about them, we did run this experiment with cell phones. First it was SMS messages, commonly used to cost $0.10 per message. Still the case for a small group of people, and some may seek out pay as you go plans to optimize their bill, but for most, they prefer to just pay a little more monthly it seems and not worry about being billed for each one. (I know it's not a perfect correlation, but it is probably the largest scale study of pay as you go vs. other options that we have.)

I've been waiting (both with anticipation and dread) for a day when micro-payments are ubiquitous, as I think it's the only way to compete with the subscription and ad business models. I just don't know if people will really accept it given previous examples of it have played out. But I still hope someone gets it right, and I can pay 5c to read a newspaper article without needing to subscribe, and things like that.