What is a trade-in credit? At&t?

This is what is says basically "Trade-in Value: $300 value for iPhone 5s and $200 value for other eligible iPhones. In AT&T-owned retail stores trade-in will instantly receive value as a private label AT&T "

So i don't understand at all. If i turn in my barely scratched iphone 5s, i will get $300 as in cash or into my credit card. That means i will be $300 richer, in my hand or in my bank? I want to buy a iphone6, $200, so i will save $100 without spending a cent on the iphone6 just by returning my 5s to them?

Trade in credit is not cash or a refund. Its to be used toward a newer, more expensive phone. Or for an extra battery. Maybe a store credit. (Not good toward your phone bill or internet bill)

Phone prices are subsidzed based on the contract length so that is a factor too.