Morgan Stanely had a fifteen year old intern write a note on teenagers media usage and got quite some media coverage of it. I think Swedish 14-year-old Gustav Holmström's blog post (sv) on the subject about Swedish youth's media habits is at least as interesting.
Gustav's article in short: people use SMS + Bilddagboken + MSN, free is good (only pay for World of Warcraft), and the mobile (SonyEricsson, no-one has an iPhone) is really important.
Some quick thoughts:
* Teenagers have a lot of time and little cash. Spending time to get something for free makes a lot of sense.
* Local language matters
* Goods/one off-payments is most of the time a better way than services/subscriptions to get paid