CTR CTLR INTERVENED ON THE DSCNT OF AN ACR LTT TO QUESTION ITS ALT ASSIGNMENT AND THEN SUBSEQUENTLY CONFIRMED THE SAME ALT AS ORIGINALLY GIVEN TO THE FLC.

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ENRTE FROM PHL TO BDR AT 13000 FT IN THE PROX OF PLUME INTXN ON VECTOR 139; WE RECEIVE A VECTOR OF 120 DEGS. FLYING THE 120 DEG HDG WE WERE ISSUED A DSCNT TO 11000 FT. DURING THE DSCNT WE RECEIVED ANOTHER VECTOR OF 040 DEGS. PASSING THROUGH 12000 FT WE NOTICED TFC PASSING OFF OUR IMMEDIATE L; AT WHICH TIME ATC REQUESTED OUR ALT; TO WHICH I RESPONDED 11900 FT FOR 11000 WITH TFC IN SIGHT. UPON QUESTIONING ATC AS TO THE ALT THEY SHOWED US TO BE AT; THERE WAS A PAUSE THEN A RESPONSE OF 13000 FT; TO WHICH I EXPLAINED WE WERE GIVEN A CLRNC FROM 13000 FT TO 11000 FT WHICH IS WHAT I READ BACK TO ATC. WE WERE THEN TOLD TO MAINTAIN THE ORIGINAL REQUEST OF 11000. SOME CONFUSION COULD HAVE RESULTED FROM THE FACT THAT THERE WAS ALSO A COMPANY ACFT WITH SIMILAR CALL SIGN ON THE SAME RTING; BUT AT A HIGHER ALT; AT THE SAME TIME. SUPPLEMENTAL INFO FROM ACN 273897: I BELIEVE THE CTLR CONFUSED THE 2 FLT NUMBERS AND ISSUED US A CLRNC INTENDED FOR ANOTHER ACFT. I BASE THIS ON THE CTLR'S RESPONSE TO OUR QUESTIONS; THE SOUND OF CONFUSION IN HER VOICE AND THE FACT THAT A NEW CTLR STARTED IMMEDIATELY AFTER THE CONFLICT. WE ARE NOTIFYING OUR COMPANY OF THE SIMILAR SOUNDING CALL SIGNS ON THE SAME RTE.