By opting in for the Direct Carrier Billing service, T-Mobile users will now have the convenience of charging their wireless account when paying for media downloads, online subscriptions, virtual currency, and pretty much anything else that would have otherwise required them to use their credit cards instead. Thanks to a two-step authentication method, the carrier promises that the process will be secure enough to eliminate the chance of unexpected charges ending up on your statement at the end of the month. Just in case, however, all online purchases will be outlined in detail on the customer's monthly bill.
The Direct Carrier Billing service will get its extended payment features by the end of this month and will be available at no extra charge. Just don't get too carried away when buying all those Farmville credits.
source: T-Mobile via Engadget