It looks like Straight Talk offers the iPhone 5 for their service (which would probably mean you could get it at Walmart), but because of the nature of their service, they are not a carrier that offers the newer model phones. So no, you will not be able to get a 5S or 5c through Straight Talk or Walmart in that fashion. You COULD however buy one outright from Apple at full retail price and then use it on Straight Talk.
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