http://www.walmart.com/ip/Walmart-F...GB-Prepaid-with-Retina-Display-Black/26011015 $399 for a new iPhone 5 is still better than the price for a $549 iPhone 5c (with basically the same specs). My question is, can I pop in a T-Mobile or AT&T SIM card and will it work? My understanding is that the Walmart Family Mobile service is based on T-Mobile's network. Or is it actually locked only to Walmart Family Mobile? Thanks!