Carrier billing lets you pay for things like apps or subscriptions by adding...

https://www.bookmark-tango.win/carrier-billing-lets-you-buy-apps-games-or-subscriptions-and-charge-them

Carrier billing lets you pay for things like apps or subscriptions by adding the cost to your phone bill. If you have a monthly plan, the charge appears on your next bill. With pay-as-you-go, the amount is taken from your available credit