CREATE TABLE table_24418525_1 (callsign VARCHAR, coverage VARCHAR)

when coverage is dumaguete central visayas region, what is the callsign?
SELECT callsign FROM table_24418525_1 WHERE coverage = "Dumaguete Central Visayas Region"
SELECT "callsign" FROM "table_24418525_1" WHERE "Dumaguete Central Visayas Region" = "coverage"