Can I buy an iPhone 5 from Walmart and add it to my plan at the AT&T store?

I want to add a line and I want to add an iPhone 5. The iPhone 5 is cheaper in Walmart and the data plan I want is not availiable through Walmart's AT&T kiosk.
(not unlocked)

AT&T would be your best source for an accurate answer.

As long as you aren't buying the Straight Talk iPhone, then yes, it will work.