That's what a rep told me but when doing the checkout on a 5S for testing I ciould not find anywhere saying I had to give them my phone. My contract ends 10/4 so it's a bit silly to give them my phone
Edit: I just redid it and you have to go all the way to the page right before confirming the order (putting in credit card, etc etc etc.) before it tells you one line in red "You have to return the device that was originally activated on the line within 14 days, or a fee up to $200 will be charged"