Carrier billing lets you buy apps, games, or digital content and charge the...

https://dibz.me/blog/why-do-carriers-cap-carrier-billing-daily-or-monthly-1245

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