ON VECTORS TO ATL ILS RWY 27L; B757 FLT CREW INCORRECTLY SET WRONG FREQ; EVENTUALLY REMAINING ON TWR FREQ FOR VECTORS AND LNDG CLRNC. CAPT DISCUSSES INCIDENT WITH A80 SUPVR.

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WHILE ON APCH TO ATL RWY 27L; 320 DEG HDG; 5000 FT; FO FLYING; APCH CTL SWITCHED US TO A NEW FREQ. AFTER CHKING IN; I MISTAKENLY PUT IN THE TWR FREQ OVER THE LAST ASSIGNED APCH CTL FREQ. REALIZING WE NEEDED A LOWER ALT; I DISCOVERED MY MISTAKE AND SWITCHED BACK TO THE LAST ASSIGNED FREQ. THEY GAVE US A TURN AND A LOWER ALT (360 DEGS; 3000 FT) AND A NEW FREQ WHICH I MANAGED TO GET WRONG. AFTER NOT BEING ABLE TO REACH ANYONE AND WITH THE ARPT GETTING CLOSER; I CONTACTED ATL TWR FREQ AND ASKED THEM FOR THE RIGHT FREQ. THEY TOLD US TO STAY WITH THEM; ASKED IF WE SAW THE RWY AND CLRED US TO LAND. ON THE GND; I WAS ASKED TO CALL TRACON. IN MY CONVERSATION WITH THEM; THEY WERE CONCERNED AS TO WHERE WE HAD GONE (ATL TWR APPARENTLY DID NOT TELL THEM THAT THEY HAD US) AND ADVISED ME THAT THEY WERE ALSO CONCERNED BECAUSE WE WERE ON A HDG TOWARD N SIDE TFC AND THEY COULD NOT GET A HOLD OF US. I ADVISED THEM WHAT I HAD DONE AND THAT IT WAS MY MISTAKE. THEY ASKED THAT I BE MORE CAREFUL IN THE FUTURE BUT UNDERSTOOD HOW THE MISTAKE COULD BE MADE.