You can get GoPhone refills directly through AT&T, through retail stores, and through various online stores. Your GoPhone is refilled by activating an airtime pin code, and these codes are of the same format whether you get them directly from AT&T, from a physical refill card that you bought at a retail store like Walmart or Target or your local convenience or from other online sites.
GoPhone airtime cards come in denominations of $15, $25, $50 and $100. The $15 card expires after 30 days after you add the minutes, and the $25 card expires 90 days.
If you buy directly from AT&T you can use your AT&T account to store your details so that it’s quick and easy to add minutes. In addition, if you know you will add a certain number of minutes on a regular basis, you can sign up for the Auto-Refill option which give you a $5 bonus with every refill.
You can go to almost any big box store like Walmart, or any Supermarket, or even any convenience store and pick up a physical GoPhone airtime card. This card is usually activated at the register when you purchase it. After that you scratch off the back of the card to reveal the airtime pin, and use that to officially add the minutes to your phone.
At most, you can save a few cents when buying airtime refills from retail stores. For example, Walmart may sell a $25 airtime card for something like $24.88, so you would end up saving 12 cents.
You can get online airtime refills from other sites as well. In the case of GoPhone, you can go to ComFi.com to get GoPhone refills.
So your best options for saving money are either to sign up for the auto refill option from AT&T to get a $5 bonus or save a few cents from retail stores.