I signed a contract for an LG phone years ago, with a deposit of W40,000. My SKY phone was great.
Because I was on an E2 visa, they wouldn't like me sign up unless a Korean co-signed.
I signed a new contract with SK and I could do it myself, but they took W200k for the deposit. They just required my ARC. I've been really pleased with their 서비스 (service). Free phone too.