Yup, because that's exactly what I had to do when the stupid setup menu wouldn't accept my email address and password combo in the "replace existing line" option for ATT. After verifying that my email and password were both correct, I figured either Apples or ATT's servers were stupid, pulled the sim out of my original Air and popped it into the Air 2. Five bars, no problems. If you're only getting one bar in a location that was giving your old model full bars, it's more likely you've got a bad unit and you should take it back while they still have replacements in stock. Bad reception is not a sim issue, it's and antenna/modem issue.