Carrier billing lets you buy apps, games, or services by charging the cost...

https://brookssnewinsight.scriblorax.com/posts/can-carrier-billing-still-be-used-for-ringtones

Carrier billing lets you buy apps, games, or services by charging the cost directly to your phone bill. If you have a monthly plan, the purchase is added to your next bill. If you use pay-as-you-go credit, the amount is deducted from your balance