How to root and flash the Galaxy Note 4 AT&T version
Sim unlock (being able to use different carriers) is not bootloader unlock or root. The SM-N910A cannot be rooted. You can root the T-Mobile version (SM-N910T). Your phone will update to Marshmallow baseband version N910AUCS2EQH1 when you check for updates with an AT&amp;T sim card installed.