Carrier billing lets you pay for apps, games, or digital content by charging...

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

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