B737 FLT CREW ACCEPTS CLRNC INTENDED FOR OTHER COMPANY ACFT WITH SIMILAR SOUNDING CALL SIGN.

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IN CRUISE AT FL270; ABEAM TPA ON THE SRQ.3 STAR INTO RSW (ACR X); I RECEIVED CLRNC TO CROSS WOUNDS INTXN AT 10000 FT. I THEN REPEATED THE CLRNC; USING MY FULL CALL SIGN; AND THEN CALLED ATC -- AGAIN; TO CONFIRM THE XING ALT. I DID THIS BECAUSE THE STAR INDICATES: 'EXPECT CLRNC TO CROSS WOUNDS INTXN AT 11000 FT.' ALSO; I WANTED TO CONFIRM THE CLRNC; SINCE WE HAD A 'SIMILAR COMPANY CALL SIGN ON FREQ' (ACR Y) WHOM WE HAD BEEN FOLLOWING SINCE DEP FROM PHL. THE CTLR REPLIED 'AFFIRMATIVE' TO MY REQUEST FOR CLRNC/ALT CONFIRMATION; AND ASSIGNED A NEW FREQ TO US. WHEN I INITIALLY CONTACTED THE NEW CTLR; I STATED THAT WE WERE 'PASSING THROUGH FL230;' SINCE I HAD BEGUN MY DSCNT. THE CTLR THEN ASSIGNED US TO 'DSND TO FL180.' I THEN INFORMED ATC THAT WE'D BEGUN OUR DSCNT TO COMPLY WITH WOUNDS INTXN AT 10000 FT. HE SEEMED SURPRISED AND QUERIED 'WHO GAVE YOU THAT?' WHEN I EXPLAINED; HE STATED 'WELL; YOU MUST HAVE RECEIVED A CLRNC FOR ANOTHER ACFT.' THE CAPT THEN ASKED IF THIS WAS CAUSING A CONFLICT. THE CTLR STATED 'NO; YOU'RE OK.' I BELIEVE THAT THIS EXPERIENCE REINFORCES THE NEED FOR EXTRA VIGILANCE ON THE RADIUS; ESPECIALLY WITH 'SIMILAR COMPANY CALL SIGN' ON THE SAME FREQ.