Carrier billing lets you buy apps, games, or services and charge them directly...

https://www.bookmarking-base.win/carrier-billing-lets-you-buy-things-like-apps-or-music-and-charge-the-cost-to

Carrier billing lets you buy apps, games, or services and charge them directly to your phone bill. If you have a monthly plan, the cost appears on your next bill. For pay-as-you-go users, the amount is taken from your available credit