What is the Callsign in Brisbane with a Freq currently of 4rph?
CREATE TABLE "defunct_callsigns" (
  "callsign" text,
  "area_served" text,
  "band" text,
  "freq_currently" text,
  "purpose" text
);
SELECT "callsign" FROM "defunct_callsigns" WHERE "area_served"='brisbane' AND "freq_currently"='4rph';