In reality, the rechargeable calling card is a specialised form of a prepaid or debit account.
In reality, the system works by a user being provided with a unique "card ID" (the PIN).
After transferring funds to the card company, the ID can be provided electronically by email, by SMS, over the internet, a coupon printed by a cash register at a store, or any other way.
Calling cards began to gain popularity around the world and they turned into a multimillion-dollar industry.
It was an instant hit, selling thousands a day on the subway systems in Tokyo and Osaka, various other companies began to get involved and released their variants.