REPLY TO WRONG CALL SIGN.

Narrative

WE WERE FLYING THE BOIDS 4 ARR INTO DFW. OUR CALL SIGN WAS XY254 THERE WAS ALSO A WXZ664 AHEAD OF US ON FREQ. THE CTR CTLR TOLD WXZ664 TO CROSS 50 MI W OF BPR AT FL240; WXZ664 RESPONDED. NOW; IN RETROSPECT; HE THEN TOLD XY254 TO DO THE SAME; BUT WXZ664 ANSWERED THE XMISSION FOR US AND SAID 'ROGER.' I WASN'T SURE AT THE TIME IF THAT CALL HAD BEEN FOR US BUT I DIDN'T QUESTION THE CTLR (MY MISTAKE). I ASKED THE CAPT IF THAT CALL WAS FOR US BUT HE SAID 'NO; THAT WAS FOR WXZ664.' AT 67 DME OUT FROM BPR; THE CTLR SAID 'XY254 START YOUR DSCNT.' AS I KEYED THE MICROPHONE TO REPLY; THE OTHER ACFT AGAIN TOOK THE CALL; REPLYING 'WXZ664 IS IN A DSCNT.' I IMMEDIATELY QUERIED THE CTLRS; AND TOLD HIM WE (XY254) HAD NO DSCNT CLRNC. THE CTLR THEN CLRED US TO FL240. WE IMMEDIATELY PUT THE ACFT INTO A MAX RATE DSCNT; MAKING THE XING RESTRICTION; BARELY. ON THE NEXT FREQ; THE CTLR ASKED US IF WE COULD MAKE THE RHOME INTXN AT 9000 FT. WE REPLIED THAT WE COULD IF WE COULD KEEP OUR SPD UP IN THE DSCNT. CTR APPROVED THE SPD REQUEST; BUT ENDED UP VECTORING US OFF THE ARR BECAUSE OUR INCREASED SPD ENCROACHED ON THE ACFT ON THE ARR IN FRONT OF US. (I CAN ONLY GUESS THAT THE ACFT IN FRONT OF US WAS WXZ664.) OBVIOUSLY; THE SIMILAR CALL SIGNS AND LACK OF CTLR CONFIRMATION OF WHO WAS READING BACK CLRNCS; AS WELL AS MY LACK OF QUESTIONING THE CTLR AND THE PLT OF WXZ664 USE OF NONSTANDARD READBACK TECHNIQUE ALL CONTRIBUTED TO THIS ENCOUNTER.