I got my iPhone 6 at BestBuy today and got moved to a counter back in the computer section to speed things up with the crowd (even though there really wasn't a crowd and I was already first in line and when moved to the back, had to wait even longer). Of course, the guys back there were not "mobile-trained" and kept radio-ing to the mobile guys questions. I asked if I could just take the SIM out of my iPhone 5 and put it in my iPhone 6 and they said it should work, so I did, and it seems to work (even my account on attwireless.com shows I have an iPhone 6). They didn't do anything in their system to activate my iPhone other than me put my SIM card in and turn it on. iMessaging works, data, visual voicemail, etc. Later today, I get a TXT from ATT saying that I need a new SIM card because I may not have access to all services if I use the existing SIM. I've read a little, and that may mean NFC. What else might I be missing by not using the actual SIM card that came with the 6? Thanks.