Carrier billing lets you buy apps, games, or digital content and charge the...

https://tiny-wiki.win/index.php/How_Did_Carrier_Billing_Start_with_Ringtones_and_Games%3F

Carrier billing lets you buy apps, games, or digital content and charge the cost directly to your phone bill. If you have a monthly plan, the purchase appears on your next bill. For pay-as-you-go users, the amount is deducted from your available credit