It's impossible because mobile card is already airtime...meaning once it was just bought for some money as any other goods..just like a ticket it is the utility for corresponding money. So now the only way to change to money is to resell it for customers or the people you know.....no more interconversion of cash and airtime. More clearly airtime is just like a mango you bought for some money...you can use to gain its utility or resell for corresponding value....but you don't have interconversion unit 🤷‍♂