Bootloader unlockable phone on AT&T?

[pantsaregood]

I'm currently using an international Nokia Lumia 1520 with AT&T's LTE bands. It looks like the AT&T Galaxy S6 has been rooted but not bootloader unlocked as of now. The One M9 appears underwhelming overall. The Nexus 6 can be rooted and unlocked pretty easily, though.

Do I have any other options for phones on AT&T? If I'm jumping ship to Android, I don't want to be at the mercy of AT&T for software updates if at all possible.

 

[Rukbat]

The Global S6 (if you like the S6) should work on AT&T - that's what most people at the local AT&T store are using, global versions of Samsung phones. You want the SM-G920F.