What ‘nationwide’ means
T-money works as a stored-value transport card across normal participating buses and subways. It does not turn separately ticketed KTX, express, intercity or reserved services into unlimited travel, and each operator’s purchase flow still applies.
Why multi-city travellers often keep T-money
A short-term Climate Card is tied to covered Seoul transport. Keeping T-money gives the same traveller a fallback for the airport, excluded Seoul rides and the Busan portion without buying a new transport concept in each city.
How much to load
Estimate Busan paid journey groups separately, add them to excluded Seoul rides, and load in stages. The finder recommends a combination when a Climate pass saves money in Seoul but the itinerary continues elsewhere.