I think that a lot of trials are underaged. They don't have access to their own creditcard.
You don't think expensive, but maybe they and their parents does?
I totally support that people are able to pay with SMS & Telephone. That's totally the right direction to go, but I think it's too hidden. I know a lot of people who never knew that you could buy gold with just an SMS.
and i'm really rooting for that Graal will be cheaper some day.