http://www.walmart.com/ip/Walmart-Family-Mobile-Apple-iPhone-5-16GB-Prepaid-with-Retina-Display-Black/26011015 I already have a T-mobile family plan. Currently Shopping for new phones. Walmart is offering $399 for a new iPhone 5 which is better than the price for a $549 iPhone 5c (with basically the same specs). My question is, can I pop in a T-Mobile 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!