What is the callsign when power kw is 25kw?
CREATE TABLE "table1_23915973_1" (
  "branding" text,
  "callsign" text,
  "frequency" text,
  "power_k_w" text,
  "coverage" text
);
SELECT "callsign" FROM "table1_23915973_1" WHERE "power_k_w"='25kW';