I used another line on my accounts eligibility to upgrade from the 5 to the 5s. I believe when I went from the 4 to the 4s, I just inserted the sim from my 4 into the 4s and that worked and didnt screw up the line I used the upgrade for. I am awaiting my 5s to deliver today and was wondering if that would still be the case with swapping my sim from my 5 to the 5s instead of having to go to ATT to get my phone activated since it was purchased for a different phone number. Anyone tried this? Did I even make sense with what I was asking?