Question about iphone 5 and buying it at a non apple store?

My contract has ended with at&t I have the iphone 4S. Well I saw target advertising there trade in and entered my phone info and it said I could get 202.00. If I were to get it thru their could I then go to apple store within 30 days and get the apple care+ protection? Or do both of them have to be purchased from Apple?