Carrier billing lets you buy apps, games, or digital content by charging the...

https://list-wiki.win/index.php/What_Does_Pay_by_Phone_Billing_Mean%3F

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