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

https://extra-wiki.win/index.php/Is_Pay_by_Phone_Billing_the_Same_as_a_Mobile_Wallet%3F

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 purchase appears on your next bill. For pay-as-you-go users, it’s deducted from your available credit