Can I take a phone call on the subway?
Short answer
Yes, quietly. The operator's own etiquette list asks for vibrate mode and a lowered voice, not for silence.
What the operator actually asks
Seoul Metro publishes a list of basic etiquette, and the phone item is specific: switch to vibration mode, and keep your voice down while on the phone. Taking the call is not the problem.
A separate item on the same list asks passengers not to run or speak aloud on trains. So the concern is volume in general, and a loud conversation with the person next to you sits under the same heading as a loud call.
The rest of the list
Let passengers get off before you board, and do not push on a crowded train. Offer your seat to pregnant women, people travelling with children, and people with disabilities.
In the stations, keep to the right as you walk, and do not walk or run on the escalators. These are the items that describe how the crowd moves, and following them is most of what looks like local competence.
How this reads in practice
A carriage here is not silent, and nobody will react to a short call taken at a normal indoor volume. The bar is closer to "do not make yourself audible across the car" than to "do not speak".
If the call needs real conversation, the same instinct that applies anywhere applies here: get off at the next station rather than hold it for ten stops.
Good to know
- Vibrate mode and a lowered voice — calls themselves are allowed
- Speaking aloud on the train is on the same etiquette list as loud calls
Phone calls are what is being avoided, not conversation. Keep the phone on silent, and on a long-distance train take the call between cars.