My iphone 4S has finally bit the dust. I currently live in South Korea but will be moving back to the States in 2 months. If I buy an iphone 6 here in Korea will I be able to use it with Verizon's prepaid plan option when I move back?
The IMEI number will not be in Verizon's database, and this will cause you problems even if you can get it working. It is not advisable.
IF you are purchasing the unlocked sim free version from Apple, (A1586 or A1524) they will work on any carrier including Verizon.
this is the international version and should be available in South Korea.
as far as I know the international version of the iPhone 6/6+ have been white listed by Verizon.