So my questions would be:
Are you planning to come back to the US a lot during that year?
Are you going to keep a US phone on contract during that time?
If you don't need a US phone a lot, and don't need people to be able to call you on your existing US number (which won't work with a foreign SIM anyway) I would suggest that you buy a phone in South Korea and use a prepay in the US until you relocate back. There should be some good phones there (given that major phone producers are based there!) and they would work with the networks, whereas some people report trouble using certain SIMs with the D2G.
Caveat: I have no knowledge of how hard/easy it is to buy phones there, and what terms (contract/prepay) are available.