Getting a Cell Phone
I would highly recommend that you get a smart phone. It is so much easier to navigate around the city with a smart phone. Don't worry about the amount of texts are included in the plan because once you get data service, you can download an app called Kakao that almost everyone in Korea uses. It's a free texting application. You can even make free calls to anyone using Kakao (including your friends at home)!
Olleh (KT), SK, and LG are three big cellular companies. I found the prices of phones and plans were pretty much similar. I went with KT just because they don't charge you a cancellation fee for when you leave the country if you are breaking the contract. I only planned on staying for a year in Korea but signed a 2 year contract because the phone would be free. When the year is up and I cancel my contract, I would need to pay the difference of the cost of my phone.
I suggest that you go to a global store because they can speak English. I had a coworker go with me to a phone store that did not speak English and there were problems with my phone. That meant that my co-worker had to go with me to the store several times which was inconvenient.
KT has a global store in Itaewon and in Gangnam. The Gangnam store is huge and has a great selection of phones.
KT Itaewon http://expatblog.kt.com/14
Address: 1st Floor, 736-11 Hannam-dong, Yongsan-gu, Seoul
서울특별시 용산구 한남동 736-11 (1층)
Phone: (02) 793-9010
Languages Spoken: Korean, English, Japanese
How to Get There: Take the subway to Itaewon Station (Line 6, Exit 3). Walk approximately 100 meters towards the Itaewon Fire Station. The Store is located on the right, past the GS Caltex.
KT Gangnam http://expatblog.kt.com/33
Address: 824-21 Yeoksam-dong, Gangnam-gu, Seoul
서울특별시 강남구 역삼동 824-21 상경빌딩
Phone: (02) 558-5115
Languages Spoken: Korean, English
How to Get There: Take the subway to Gangnam Station (Line 2, Exit 1). Walk straight approximately 100 meters. Olleh Avenue is located on the Kookkiwon Intersection.