WITH SIMILAR CALL SIGNS ON THE FREQ AN ACR IS QUESTIONED TWICE ABOUT NON COMPLIANCE WITH BOTH HEADING AND ALT CLRNCS THAT THEY HAVE NEITHER HEARD NOR ACKNOWLEDGED. ONE CREW MEMBER WAS OFF FREQ FOR PART OF THE TIME ON ANOTHER RADIO.

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CHKED ON WITH SYR APCH AT 11000 FT. MY COPLT; WHO WAS WORKING THE RADIOS; WENT OFF ATC TO CALL STATION IN-RANGE. I ACKNOWLEDGED I WAS ON ATC. CTLR ISSUED INSTRUCTIONS TO ACR X WHICH WERE ACKNOWLEDGED. THEN CTLR ISSUED A WARNING THAT WE WERE ALSO ON FREQ AS ACR Y. WE BOTH ACKNOWLEDGED. LATER; THE CTLR ASKED IF WE HAD STARTED DOWN TO 4000 FT. I RESPONDED THAT WE HAD NOT RECEIVED A CLRNC TO 4000 FT (MY ALT SELECTOR WAS STILL SET AT 11000 FT). SHE SAID WE HAD ACKNOWLEDGED THE CLRNC. IN FACT; I HAD NOT SPOKEN ON THE RADIO EXCEPT TO ACKNOWLEDGE THE CALL ABOUT ACR X. WE INITIATED THE DSCNT TO 4000 FT. BY NOW; MY COPLT WAS BACK ON ATC. AT AROUND 9000 FT IN THE DSCNT THE CTLR ASKED IF WE WERE TURNING TO HEADING 010 DEGS. I RESPONDED THAT WE WERE STILL ON THE AIRWAY; AS LAST CLRED. SHE INSISTED THAT WE HAD ACKNOWLEDGED THE CLRNC TO TURN TO 010 DEGS. ONCE AGAIN; WE HAD NOT SPOKEN ABOUT A HEADING CHANGE ON THE RADIO; AND THE NAVAIDS AND RNAV SYS WERE STILL SET ON THE AIRWAY. I HONESTLY DON'T KNOW WHAT HAPPENED. IT IS POSSIBLE THAT WE (OR I) MISSED HEARING A CLRNC; BUT I KNOW THAT WE DID NOT ACKNOWLEDGE EITHER A DSCNT OR TURN. I SUSPECT THERE WAS CONFUSION AS A RESULT OF THE SIMILAR SOUNDING FLT NUMBERS -- POSSIBLY SOMEONE ELSE ACKNOWLEDGED OUR 'CLRNC;' BUT I DID NOT HEAR SUCH AN EXCHANGE. IT WOULD BE BETTER IF 1 PLT DID NOT HAVE TO LEAVE THE FREQ FOR REQUIRED CALLS TO COMPANY. I AM ALWAYS WARY WITHOUT 2 OF US LISTENING.