According to this post, it seems that you can use your credit card as T-money, and just tap your card on the subway gate to pass it through.
Much like Singapore's ez-link card, T-money is a rechargeable stored-value card with a smart chip for fare deduction. The chip has been modified to fit credit cards, debit cards and even mobile phone SIM cards - which means people can tap their phones to take the bus.
It is amazing. I want to use my credit card as T-money.
However, how can I do it? My guess is that you must get issued a card in the first place that is compatible with T-Money; at least that is the case in Japan, where there is a credit card issued by JR-East which is compatible with Suica.
Or if this is the case in Singapore, you can link your credit card to your transportation card (ez-link), and top up your ez-link automatically when the balance runs out.
So is it possible to get issued the card? I can stay for a few months if it is needed, though I enter it with 90 days of free-visa requirement.
I don't mind what brand it is (though UnionPay or MasterCard is preferable as I don't have it), or don't need much limit. All the things I need is to get through the gate when I don't have enough balance on T-Money.