Microsoft will be adding the option for consumers to utilise gift cards on the Windows Store and Xbox Live, but the company has already enabled the payment gateway on the Windows Phone Store



From WPCentral:

Adding a gift card to the Wallet, a feature in Windows Phone 8, smartphone owners can use the cards to charge app, music and media purchases. It's similar to the current Microsoft Account system, where people can redeem codes to add to their balance e.g. Bing Rewards in the US or the $25 Store credit for the Verizon Lumia 928.

  Microsoft adds gift cards as method of payment to Wallet for Windows Phone 8