Pay-by-phone transactions make it easy to buy apps, games, or subscriptions...

https://smart-wiki.win/index.php/What_is_Direct_Carrier_Billing_(DCB)_in_Plain_English%3F

Pay-by-phone transactions make it easy to buy apps, games, or subscriptions without a card. Charges go directly to your monthly phone bill or use prepaid credit, so you can keep track of spending in one place