T-Money Sim Card

Hiya
I live in Korea and would like to pay for the tube and busses by my mobile phone (My network is KT). I've heard that there exists T-Money Sim Card and I was wondering if I get one of those, can I transfer my current sim balance (about 50.000 won) into the new sim and use it to pay for the tube or I have to top it up separately to pay for the tube?
Cheers

Any comments?