LGT SAYS COMPANY FLT WITH SIMILAR CALL SIGN WAS GIVEN HOLDING INSTRUCTIONS AND ACKNOWLEDGED SAME. CLTR GAVE THEM DESCENT AND SPEED RESTRICTION; THEN ASK IF THEY HAD COPIED HOLDING INSTRUCTIONS. REPORTER FEELS THAT ATC MAY HAVE CONFUSED THE CALL SIGN AND CLRNC.

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OUR FLT WAS AGC. THERE WAS ALSO A COMPANY FLT ABC ON FREQ. WE WERE WITHIN 40 NM OF THE PONTIAC VOR WHEN ATC ISSUED A HOLD CLRNC FOR COMPANY ABC TO HOLD AT THE PONTIAC VOR SW LEFT TURNS; 20 MI LEGS; FL250 XX00Z. AS IT TURNED OUT ABC WAS BEHIND US IN THE SEQUENCE INTO O'HARE. ABC READ BACK CLRNC. OUR FLT AGC WAS ISSUED A DSCNT CLRNC TO FL240 AND TO MAINTAIN 270 KTS IAS. AS WE PASSED THE 12 DME ARC ON THE ARWY CENTER ASKED US IF WE HAD RECEIVED OUR HOLDING CLRNC FOR FL250. WE RESPONDED THAT COMPANY ABC HAD BEEN ISSUED THAT CLRNC AND THAT WE WERE AT OUR CLRED ALT OF FL240 AT 270 KTS. CHICAGO CENTER THEN ISSUED US; AGC; THE ABOVE HOLDING INSTRUCTIONS. WE ACKNOWLEDGED AND CLBED BACK TO FL250 AT ATC REQUEST. THEIR WAS NO CONFLICT WITH TFC MENTIONED BY ATC OR OBSERVED BY US. CENTER OBVIOUSLY ISSUED THE CLRNC TO ABC BY ERROR. ABC READ BACK THIS CLRNC AND WE HEARD THIS ALL VERY CLEARLY. WE AGC FOLLOWED OUR ATC CLRNC TO THE LETTER; BUT WERE REALLY NOT SUPPOSED TO BE WHERE WE WERE CLRED. HOWEVER; WE HAD NO WAY OF KNOWING THE CLRNC PREVIOUSLY ISSUED TO ABC WAS FOR US. THE FLT PROGRESSED UNEVENTFULLY AND SAFELY TO O'HARE.