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

https://melissazxlth.gumroad.com/p/how-do-i-pay-with-carrier-billing-on-a-monthly-plan

Carrier billing lets you buy digital goods or services and have the cost added to your monthly phone bill or taken from your pay-as-you-go credit. This means no need for credit cards or separate accounts