Pay-by-phone lets you buy digital goods and services by charging the amount...

https://sierra-wiki.win/index.php/Carrier_Billing_vs_Credit_Card_for_Online_Purchases:_Which_Checkout_Method_Wins%3F

Pay-by-phone lets you buy digital goods and services by charging the amount directly to your monthly phone bill or prepaid credit. It’s a simple way to pay without needing a card or bank account