Okay, so I'm wanting to add 'credits' to this game and an option is using your phone to pay, does this mean it deducts the phone credit you currently have?

The location and the phone company you use makes a difference. Normally when you pay by phone, you provide them a credit card to charge it to.

When adding game credits, the credits are either applied to your phone bill (ie: it will increase the total of the credits purchased) or are deducted from your prepaid balance.

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