Ok, so out of curiosity I put a different sim into my AT&T iPhone 5S and when I did I got a "Activation Required" screen, and it said "This iPhone is currently linked to an Apple ID (j*********@i****.com). Sign in with the Apple ID that was used to set up this iPhone." You can't bypass, even if you remove the sim card. And then it asked for my Apple ID & Password (Which I logged in with). I just tried this on my brother's 5S as well and it does the same thing. Does anybody know what's up with this? It seems like a cool feature incase you lose you'r 5S but didn't have Find my iPhone feature and somebody try's to put a diff Sim Card to use your iPhone. My 5S has a password but my brother's didn't. Have only tried this on the 5S, might be the same with the 5,4S, or 4. Would be nice if other ppl confirm it does this on other iPhone running iOS 7. EDIT: This was with a T-Mobile US Sim Card.