LGT BEGAN DESCENT WITHOUT RECEIVING CLRNC.

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OUR FLT NUMBER WAS ABC. A COMPANY FLT NUMBER WAS AAC. ON 2 DIFFERENT OCCASIONS; I RESPONDED FOR AAC. ONCE; I VERIFIED THE CALL AND PREVENTED THE ERROR. ON THE SECOND OCCASION; THE FE CAUGHT MY RESPONSE TO CENTER AND IT WAS CORRECTED W/O RESPONDING TO THE ACTION REQUESTED. AS BOTH AAC AND ABC SWITCHED TO APCH THE PROB CONTINUED AND BECAME MORE CRITICAL. EACH OF US WERE ON SIMILAR TRACKS FOR THE S LNDG. AS SUCH; SIMILAR VECTORS AND ALTS WERE BEING XMITTED. WE WERE IN TRAIL OF AAC AND VMC WITH THE ARPT IN SIGHT. APCH HAD KEPT US HIGH AND WE WERE EXPEDITING A LOWER ALT WITH AN APCH CLRNC AT ANY TIME. APCH ISSUED THE FOLLOWING CLRNC 'TURN LEFT TO 210; MAINTAIN 3000' UNTIL ESTABLISHED; 170 KTS TO PENZZ AND CONTACT THE TWR AT PENZZ 128.2.' KNOWING THAT WE WERE HIGH; THE CAPT BEGAN EXECUTING THE INSTRUCTIONS. BEFORE I READ THE CLRNC BACK; I ASKED IF THAT WAS FOR US; ABC; ONLY BECAUSE WE HAD TROUBLE WITH IT EARLIER. APCH INFORMED US THAT IT WAS NOT. WE DIDN'T VIOLATE ANY RULES BUT UNDER DIFFERENT CONDITIONS; IT MAY HAVE BEEN HAZARDOUS. I TALKED WITH THE OTHER CREW; AAC; AND THEY FOUND THE SAME PROB WITH THE CALL SIGN. I RECOMMEND THAT AIRLINES BE MADE AWARE OF THIS PROB WHEN NUMBERING FLTS. I FIND THAT ON A 3 DIGIT FLT NUMBER; THE FIRST AND THIRD NUMBER ARE MOST READILY HEARD AND THE MIDDLE DIGIT GETS WASHED OUT.