ACR ATR72 FLC FAILED TO VERIFY CLRNC TO LAND PRIOR TO TOUCHDOWN. FLC REALIZE THEY HAD RADIO STILL TUNED TO APCH CTL WHEN TURNING OFF RWY. CONVERSATION WITH TWR SUPVR CONFIRMED THEY WERE CLRED TO LAND; EVEN THOUGH THEY DID NOT ACKNOWLEDGE CLRNC.

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IT WAS THE 7TH LEG OF THE 2ND DAY OF A 2-DAY TRIP IN WHICH WE RECEIVED AN 8 HR REDUCED REST OVERNIGHT. WE WERE INBOUND TO ATLANTA ON THE LAST LEG AND THE ENTIRE CREW WAS EXHAUSTED FROM OUR HORRIBLE SCHEDULE. IT WAS A NORMAL VISUAL APCH TO RWY 26R IN ATL WHERE WE WERE TOLD TO CONTACT TWR AT THE MARKER. THE CAPT WAS HANDLING THE RADIOS AS I WAS THE PF. THERE WAS A DISTR IN THE COCKPIT AND I THOUGHT THE CAPT HAD COMPLETED THE 500 FT CHK WHICH INCLUDES VERIFYING CLRED TO LAND; BUT I GUESS NOT. WE LANDED WHILE STILL ON APCH FREQ. UPON EXITING THE RWY; THE CAPT REALIZED IT AND SWITCHED TO TWR. WE THEN CONTINUED TO THE GATE AS NORMAL. WE CALLED THE TWR BY PHONE AFTERWARDS AND THE TWR CHIEF SAID THERE WAS NO CONFLICT AT ALL; AND IN FACT WE WERE CLRED TO LAND; WE JUST DIDN'T ACKNOWLEDGE IT. I THINK THE MAJOR PROB IS IN THE SCHEDULE WE HAD FLOWN; OUR FATIGUE WAS CERTAINLY A CONTRIBUTING FACTOR. I THINK SAFETY COULD BE GREATLY INCREASED IF SCHEDULES ALLOWED PROPER REST AT OVERNIGHTS AND CONSIDERED HUMAN FACTORS A LITTLE BIT MORE.