phones are really really important, not just to communicate with your signif other, but also your korean teachers. sometimes i need to call my co-teacher and vice versa.
i didn't get a contract phone 'cause i heard that they were expensive and that you need to sign a 2 year contract. but some friends of mine have contract phones for only 1 year. they say it's expensive, but they do have nice phones.
my phone is a 'pay as you go' phone: i can't rememeber how much i bought it for, though. it was cheap, i remember that. after you buy one though, you "buy" minutes. when you are running low on minutes you receive a text telling you to "re-charge" your minutes. i always buy 10,000 Won worth of minutes and it lasts me about 2 months. to re-charge my phone i go to SK telecom store and hand over my phone and ask "re-charge?" and mime calling someone. it works for the most part.
i guess i lucked out in buying a 'pay as you go' phone: someone was selling them nearby when i was doing orientation, so it was really easy. as for finding one on your own, i'm not too sure where you can go. maybe the SK telecom store? or ask your co-teacher.
your phone from home won't work unless it has some sort of special chip in it. look up what coverage you have and also korean phone info online. i can't remember what the requirments were for phones to work in korea, but the two US phones i tried failed