Back in August:
All subscription services (including but not limited to WAP services using premium text as a billing mechanism and Web-based registration) require opt-in using a subscriber-initiated MO SMS from the handset that will be charged.
Before that it worked:
Enter mobile number > Receive PIN code > Enter PIN code > Receive Download
So if people dont confirm transactions then it doesnt go through, it seems a lot of people dont bother so I still get plenty of click-thrus but no sales.