A CL65 CREW TAKES THE CLRNC MEANT FOR ANOTHER COMPANY FLT AND STARTS DSCNT INTO THE ALT OF ANOTHER FLT; A J31. BOTH FLCS HAD RESPONDED TO THE SAME CLRNC.

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I WAS THE PF INBOUND TO CLT ON THE SHINE 5 ARR. OUR CALL SIGN WAS 'ACR X ABCD.' ATC INSTRUCTED COMPANY ACFT 'ACR X ABEF' TO DSND TO 10000 FT. BOTH THE CAPT AND I MISTOOK THE CLRNC TO BE OURS. I WAS DSNDING THROUGH 11500 FT FROM 12000 FT WHEN A RESOLUTION CAME OVER THE TCASII. I MADE THE CORRECT EVASIVE MANEUVER AND STARTED CLBING. THE CAPT NOTIFIED ATC OF THE RESOLUTION. ATC CAME BACK AND TOLD US THE CLRNC TO DSND TO 10000 FT WAS FOR OUR COMPANY. I CONTINUED THE CLB BACK UP TO 12000 FT; OUR PREVIOUS ALT. THE FIRST PROB WAS THAT WE DID NOT LISTEN TO THE CLRNC AS CAREFULLY AS WE SHOULD HAVE; KNOWING THAT A SIMILAR CALL SIGN WAS ON THE SAME FREQ. THE OTHER PROB WAS THAT; WHEN WE READ BACK THE CLRNC; WE DID SO AT THE SAME TIME COMPANY DID. ATC DID NOT REALIZE 2 ACFT WERE TALKING OVER THE FREQ AT THE SAME TIME. EVEN THOUGH ATC MIGHT NOT HAVE HEARD OUR READBACK CLRLY; THEY MUST HAVE KNOWN SOMEONE ELSE WAS BLOCKING THE FREQ AND SHOULD HAVE INQUIRED ABOUT IT. SUPPLEMENTAL INFO FROM ACN 399832: WOULD'VE PREFERRED THE CTLR CLARIFYING THE READBACK WHEN HE HEARD 2 ACFT RESPOND. INSTEAD; HE SEEMED UNINTERESTED; EVEN WHEN THE OCCURRENCE HAPPENED.