Carrier billing lets you buy apps, games, or services and charge the cost...

https://andersonsimpressivecolumn.urbanvellum.com/posts/is-carrier-billing-the-same-as-paying-by-text-clearing-up-common-confusion

Carrier billing lets you buy apps, games, or services and charge the cost directly to your phone. Instead of using a credit card, purchases appear on your monthly phone bill or are taken from your pay-as-you-go credit