AN ATR 72 FLC ACCEPTS THE ALT CHANGE MEANT FOR ANOTHER ACR FLT WITH A SIMILAR SOUNDING CAL SIGN 15 WEST OF ATL; GA.

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INBOUND ON FLT ACR X AT 11000 FT; WE WERE SWITCHED TO ATL APCH ABOUT 8 MI FROM ATL VOR. WHEN WE CHECKED IN THERE WAS AN ACR Y ALREADY ON THE FREQ; BUT THE CTLR ON 126.9 DID NOT ADVISE US OF THE SIMILAR SOUNDING CALL SIGNS. ABOUT 5 MINS AFTER WE CHECKED IN; ACR Y CHECKED IN; AND AGAIN THE CTLR DID NOT ADVISE EITHER ACFT OF WHAT WAS NOW VERY SIMILAR CALL SIGNS. WHILE FLYING A 180 DEG HDG ABOUT 15 MI WEST OF FIELD; CTLR GAVE US A DSCNT TO 10000 FT. CAPT READ BACK CLRNC WITH HARD EMPHASIS ON 'ACR X'; AND DSCNT WAS INITIATED. DSNDING THROUGH 10700 FT CTLR ASKED US TO VERIFY THAT WE WERE LEVEL AT 11000 FT; AS WE WERE SHOWING 10700 FT. CAPT INFORMED HIM THAT WE WERE DSNDING TO 10000 FT; AND RESTATED THAT SPECIAL EMPHASIS HAD BEEN PUT ON THE 'ACR X' PART OF THE READ BACK. WE WERE INSTRUCTED TO IMMEDIATELY CLB TO 11000 FT; AND A 2000 FPM CLB WAS INITIATED BACK TO 11000 FT. ABOUT 2 MINS LATER; CTLR ASKED ACR Y TO VERIFY THAT HE WAS DSNDING; AND ACR Y RESPONDED THAT THEY HAD NOT RECEIVED A CLRNC TO DSND. THEY WERE GIVEN THE DSCNT CLRNC; AND THEN THE CTLR STATED 'OK; I SEE WHAT I DID; SORRY ABOUT THAT...' FLT WAS CONTINUED WITHOUT FURTHER INCIDENT; HOWEVER; THIS CTLR NEVER DID ADVISE OF SIMILAR SOUNDING CALL SIGNS; EVEN AFTER THE MIX UP. HIS HANDOFF TO US WAS 'ACR X CONTACT APCH ON 127.25; AND SORRY ABOUT THE MIX UP; GOOD DAY.' I CHECKED THE ACR Y COMPUTER ON LNDG AND ACR Y IS SCHEDULED TO ARRIVE IN ATL AT XA59. WE WERE SCHEDULED TO ARRIVE AT XB45 AND ACR Z IS SCHEDULED TO ARRIVE AT XC06. IT IS OBVIOUS THAT WITH JUST A SMALL VARIANCE IN ARRIVAL TIMES THIS CAN; WILL; AND DID CAUSE AT THE VERY LEAST SERIOUS CONFUSION. WE FLY THE SAME RTES DAY AFTER DAY; AND WE NORMALLY KNOW WHEN TO EXPECT TURNS; DSCNTS; FREQ CHANGES; ETC. IN THIS CASE THE DSCNT CAME AT AN UNUSUAL PLACE; SO WHEN I READ BACK THE CLRNC I PLACED SPECIAL EMPHASIS ON OUR CALL SIGN; WHICH THE CTLR EVIDENTLY DID NOT PICK UP ON. WITH A BUSY FREQ SUCH AS ATL APCH CTL; IT IS SOMEWHAT DIFFICULT TO GET A COMPLETE QUESTION IN ABOUT A CLRNC; BUT NEXT TIME THIS HAPPENS I WILL CERTAINLY TAKE THE TIME. IN ADDITION; THERE ARE 3 FLTS INTO THE ATL ARPT WITHIN 1 HR WITH SIMILAR CALL SIGNS; AND THIS NEEDS TO BE CHANGED.