Direct Carrier Billing lets you charge digital purchases to your phone bill. These digital products include: Digital games, gaming and social networking credits, music and videos. This service has been available to T-Mobile customers who use Android phones since 2009. However, Direct Carrier Billing can now be used by T-Mobile customers from any web browser (desktop, netbook, tablet or smartphone).
Direct Carrier Billing will use billing services from BilltoMobile, Boku, OpenMarket, Payfone, and Zong. Purchases will require a two-step authentication (not just a password). The service will be available later this month (August 2011).
Via CNET: T-Mobile wades into mobile payments