Is this true for all US carriers, or just ATT? Which of the 3 character groups in the CSC string determines network priority? (my U1 unlocked device is CCT/CCT/XAA).Radio is the same.
CSC for the device is the difference.
U devices are the preferred device on AT&T, and have a different software configuration than U1 devices.
IMS config is different as well as a host of other carrier specific tweaks to network settings.