Unlocked AT&T S6 and updates

I am out of the US with an unlocked AT&T S6 G920A.
Firmware is still OCE

Questions:
- Will I receive OTA updates? I have a gophone sim card, does it help?
- What if I go to the US, put the gophone sim card? Will I get OTA updates?
- Can I manually update the firmware?

Thanks!!