Will a factory unlocked iPhone 5 A1429-GSM work in S Korea & USA?

According to Apple, the model A1429 (GSM) is the one for South Korea- LTE bands 1 (2100 MHz), 3 (1800 MHz) and 5 (850 MHz).

When I return to the US in 2014 will I be able to use it on Verizon and sprint's network? I noticed that the LTE band 1, 3 and 5 are also supported by those two US carriers. However, those two carriers use a different platform/technology (CDMA).

I am positive that the A1429 GSM will use a nano sim card. What about the CDMA? Please clarify.

I am contract free as of yesterday and able to go with either of the carriers and be able to factory unlock it before my departure in January 2013. However, the hardware must work in Korea and in the US.

Another option that I am considering is a factory unlocked iPhone 4S, but I cant find a 32GB. I am very reluctant with this option as I am afraid that when I return to the US (Jan 2014) things will drastically change and I wont be able to enjoy the new advancements in the mobile tech world because I have a hardware that wont handle them.

Thank you.