A recent report produced by Juniper, was promoted by the following tagline: "more than 2bn Mobile Users Will Have Bought Digital Goods With Their Phones by 2013". This is huge.
The report seems to be well structured according to specific regions and look at things like transaction sizes and volumes. It seems as if they have done a good job to substantiate the claim. If these numbers materialise, a lot of work will have to be done by a lot of people and - for sure - this would be the biggest revolution since the invention of money.