Walmart GameCenter (officially Walmart GameCenter Magazine according to the indicia) in an ongoing magazine published by EGM Media LLC. Introduced in late 2011, the magazine grew out of Walmart's "Gamecenter" branding introduced in 2010. The magazine has maintained a schedule of 10 issues per year with print copies distributed in Walmart stores and digital issues made available via iTunes and ScreenPaper.
Contradicting this announcement press release, all issues of Walmart GameCenter - both print and digital - have been made available free of charge thus far. You can typically find the latest print issue available in the electronics section of your local Walmart. While subscriptions were mentioned in both the initial press release and each issue's indicia, they don't appear to be available.
Walmart GameCenter Index