Since the beginning of the service, users who wished to subscribe to magazine feeds, TV shows, or have access to Play Music All Access, needed a credit card on file to be charged when it came time to pay Google.
Starting recently, it appears Google has made it possible to use your Google Play balance to pay for subscriptions, such as your Google Wallet balance or Google Play balance (gift cards, survey rewards, etc.). While we are not entirely sure if the ability to pay with your Google Wallet balance is new, since we have not subscribed to any services on Google Play since the launch of All Access, the ability to subscribe to services with a gift card is entirely new.
The only downside we can see right now is that if you are already subscribed using your credit card, you will need to unsubscribe from the service, then resubscribe using your newly selected payment method. For all of you early adopters who are using All Access for only $7.99, you need not worry, as many users have stated on forums that you should not see the higher $9.99 price as long as you resubscribe quickly. However, confirming this with a Google Play support staff member may not hurt just to be safe.
Thinking about switching up your payment option? If I made enough through those surveys Google sends out, I totally would.