Can I buy an iPhone from Best Buy/WalMart as an upgrade on my plan?

I want a iPhone 5, but Sprint is out of stock and I don't want to wait 3 weeks for the shipment. If I go to Best Buy or WalMart and buy the iPhone 5 there, will they acknowledge my plan and sell me the iPhone at the price of an upgrade? If yes, do I then have to take it to Sprint to get it all situated or is everything fine from there?

As long as they're an authorized dealer for Sprint (which they should be) and they have Sprint iPhones in stock then yes.

Like the other person said, If they are a legit dealer then yeah you can, if they have them in stock. If they're a legit dealer you won't have to take it to sprint.