If you are looking to get in on the smartphone action mobileboo.com is a subsidiary of SK Telecom (SKT), which was launched in 2011 to help foreigners who want a smartphone since may shops don't have a "waygooken" procedure. I currently have a Samsung Galaxy S2 which I pay about 70,000Won a month for with 300 minutes/texts as well as unlimited data.
While this may seem pricey for some, in my opinion it is a better deal than I would get in the U.S.A. And while I did sign a 2-year contract, the price to break the contract is only 25,000WON and I must also pay the phone off but then the phone is my to keep and take with me which is a quad-band device. Which I can take with me to the U.S.A and use. If your interested I urge you to check it out, because the whole site is in plain English as well as the support when you call or email. And they even send in your device to your home so you don't have to go pick it up; they have different plans and devices like iPhone 4's, Samsung Galaxy's, and tablets. I recommend you go for the brands like Samsung and Apple's because they are better suited to use internationally unlike Sky which is really only for Korea. Basically if you can find it for sale in your home country go with one of those.
How this helps that poor soul who wants a smartphone, but not sure where to start. This is great because you won't need to hassle you Korean friends or teachers to co-sign for you. A last tip, when they ask for you to scan your passport/ bankbook you can just take a close picture with your camera as a .jpeg file and send it in.