Just following the instructions on the paper they ship with the device. Like posted above, some say keep the accessories and some say return everything plus your old phone.
I have seen so far 5 cases of these "incompetent" employees telling you to just return the phone. So far in all 5 cases, the people who kept the extra memory card and charger got billed full retail price for those items. It takes 2-3 billing cycles but there is a good chance you will get caught and billed for what you kept that you shouldn't have.
Just because they are incompetent does not mean you have the right to break the law. Pretty simple concept. Claiming you were misinformed does not nullify actions that you know are wrong. It all comes back full circle, but like I said it takes a few cycles.
This is exactly what happened to me, and I got billed for the extras even though I was told to keep everything but the phone and it was even in my notes that I was told to do this, it did take 2 billing cycles to catch up..... What a mess not worth it!!!