Default Galaxy S4 SGH-I337 never activated with the carrier, now out of the country

I bought a brand new AT&T Samsung Galaxy S4 SGH-I337, but I never activated it while in the US. Now I live in South America and cannot find a way to unlock it without it becoming region locked.
Is there anyway I can unlock this device now?
I appreciate all the help I can get, since I am desperate to use it and I cannot.

Thank you for your help!