Carrier billing lets you buy digital goods or services and charge the cost...

https://golf-wiki.win/index.php/What_Is_Direct_Carrier_Billing_and_How_Is_It_Different%3F

Carrier billing lets you buy digital goods or services and charge the cost directly to your phone bill. Whether you have a monthly plan or pay as you go, purchases either add to your regular bill or are taken from your prepaid credit