There are some misdirections in this thread.
I have returned my ip4 TWO times now, so I'm on my third one.
Each time I was given a brand new phone from the apple store.
I originally bought my phone from the att store.
I called them up and spoke with the manager, and if I feel I still want to return my phone within the 30 days, she says I am completely free to do so, it makes no difference I don't have the "original" phone, as they sold me a bad phone.
Maybe it's different with best buy or individual stores... but as least in my case I'm safe.
I originally did buy 6 ip4's though, so I always get to dangle that over att's head, if they don't let me return my one, I will return all the 5 others, so it's basically common business sense on their part.
But I didn't even have to use that when I spoke with my manager, she assured me if I was unhappy within 30 days, I can return no issues whatsoever.
I will be returning one of the 6 and downgrading to a 3gs, but the other 5 will 90% most likely stay 4's.