Foreigners and students who want cheaper phone service than the big three carriers (SKT, KT, LGU+) often turn to providers that rent the same network at lower prices. What are these called?

MVNOs, called al-tteul-pon in Korean, are budget mobile carriers that lease network capacity wholesale from the three major carriers — SKT, KT, and LGU+ — and resell it at lower prices while riding on the exact same physical network, so signal quality and coverage are identical even though the monthly bill is cheaper. This works because the big carriers have spare network capacity to lease out, and MVNOs compete purely on price and plan flexibility rather than owning infrastructure.

Payphones and roaming phones describe entirely different things: payphones are coin- or card-operated public phones, and roaming refers to using your home-country carrier's service while traveling abroad, neither of which relates to discount domestic mobile plans.

Because MVNO activation typically requires an ARC, newcomers without one yet often start on a prepaid SIM activated with just a passport, then switch to a cheaper MVNO plan once their registration card comes through.