REPLY TO WRONG CALL SIGN.

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ON ARR INTO CVG APPROX 20-30 NM SW OF THE CVG VOR AT 12000 FT INBOUND ON THE 060 DEG HDG (240 DEG RADIAL FROM CVG VOR). WE WERE ON CVG APCH CTL WHEN WE HEARD THE CTLR SAY 'ACR I NEED TO WIDEN YOU OUT; FLY HDG 350 DEGS.' I READ BACK 'ACR 350 DEGS' AND WE TURNED TO THAT HDG. APPROX 1-2 MINS LATER; THE CTLR ASKED US OUR HDG AND WHY WE HAD TURNED. I REPLIED '350 DEGS ON AN ASSIGNED HDG.' THE CTLR SAID 'TURN IMMEDIATELY TO 090 DEGS; THAT 350 DEG HDG WAS FOR AN ACFT ON ANOTHER FREQ.' WE IMMEDIATELY TURNED TO 090 DEGS. I BELIEVE THE CTLR WORKING 2 FREQS AND THE FACT THAT THERE WERE SIMILAR FLT NUMBERS ON EACH FREQ WERE THE CONTRIBUTING FACTORS. CTLRS WORKING SEPARATE FREQS MAKES IT VERY DIFFICULT FOR US TO MAINTAIN AS HIGH A SITUATIONAL AWARENESS AS WE COULD. ON A SINGLE FREQ WE ARE ABLE TO HEAR IF ANOTHER FLT ANSWERS THE CTLR'S INSTRUCTIONS WHEN WE THINK THE INSTRUCTIONS ARE FOR US. THAT RAISES A QUESTION IN OUR MINDS AND WE ARE ABLE TO ASK 'WAS THAT LAST CALL FOR US (FLT NUMBER).' ALSO THE FACT THAT 2 ACFT ANSWER AT THE SAME TIME (EACH THINKING THE INSTRUCTION WAS FOR THEM) WILL ALERT THE CTLR AND ENABLE HIM/HER TO SAY 'BLOCKED; CONFIRM FLT XXX...' AND HE CAN CONFIRM/REISSUE HIS INSTRUCTIONS. OBVIOUSLY SIMILAR FLT NUMBERS; BE IT ON A SINGLE FREQ OR SEPARATE FREQS; ARE A MAJOR DRAWBACK.