Today Apple has expanded its carrier billing system in Belgium and Norway. This is in addition to Germany, Japan, Russia, Switzerland, Taiwan, Saudi Arabia, and the United Arab Emirates. Of course, the feature is available on select carriers within the country.
This feature allows customers to pay in the iTunes Store, App Store, iBooks Store, and even for Apple Music subscriptions through their carrier. The real benefit to this is that customers would not need a credit or debit card, or even a bank and can just pay it off via their phone bill at the end of each month.
To learn how to set up carrier billing, Apple has a support document with instructions on how to do so.