I did this when I got my iPhone 5 and I had to take my phone in to the store before activating it so they could get the SIM card situation all set. This in turn made my dad's SIM (the line that I used the upgrade for) to turn off so I had to go and deliver a new SIM to him after I was done at the store. I just got off chat with a rep from AT&T and he said they've changed it to make it easier and that I can just activate the phone when it arrives. He didn't provide me with much more detail even though I continued to ask. Is there anybody who did this when the 5s came out that could shed some light?