Carrier billing lets you buy apps, songs, or subscriptions and charge the cost...

https://station-wiki.win/index.php/Carrier_Billing_vs_Credit_Card:_Which_is_Better_for_Security%3F

Carrier billing lets you buy apps, songs, or subscriptions and charge the cost directly to your phone account. The amount either appears on your monthly phone bill or is taken from your pay-as-you-go credit