COMMUTER FLC RESPONDS TO POS AND HOLD CLRNC FOR ANOTHER ACFT; CREATES CONFUSION WHEN OTHER ACFT CLRED FOR TKOF.

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WHILE #1 FOR TKOF ON 36L AT MEM; THE MEM TWR CTLR INSTRUCTED ACR FLT XAY TO 'TAXI INTO POS AND HOLD.' OUR CALL SIGN WAS 'ACR XYZ' AND MY FO RESPONDED TO THE TWR THAT 'ACR XYZ WAS TAXIING INTO POS AND HOLD ON RWY 36L.' I CLEARLY HEARD THE TWR INSTRUCTION FOR 'ACR XAY' TO TAXI INTO POS AND HOLD BUT ASSUMED THAT WHEN MY FO RESPONDED THAT 'ACR XYZ WAS TAXIING INTO POS AND HOLD' THAT THE TWR CTLR REALIZED THAT HE HAD HIS FLT PLAN STRIPS OUT OF CORRECT ORDER. THE TWR CTLR NEVER QUESTIONED OUR READBACK OF 'ACR XYZ TAXIING INTO POS AND HOLD. SO I PROCEEDED TO TAXI INTO POS AND HOLD ON RWY 36L. AFTER APPROX 20 SECONDS THE TWR CTLR THEN CLRED ACR XAY FOR TKOF. IT WAS THEN THAT WE BECAME AWARE THAT THE TWR CTLR HAD NOT HEARD OUR READBACK OF 'ACR XYZ' GOING INTO POS AND HOLD. WE THEN RESPONDED THAT 'ACR XYZ' WAS IN FACT THE FLT THAT WAS IN POS AND HOLD! THIS WAS A CLASSIC EXAMPLE OF BASIC (VERBAL) COM FAILURE BTWN 3 PEOPLE (CAPT; FO AND TWR CTLR) INVOLVED DURING THE EXCHANGE. ONCE THE TWR CTLR FIGURED OUT THAT HE HAD ACR XYZ 'IN POS AND HOLD AND NOT ACR XAY' HE POLITELY FAULTED US FOR GOING INTO POS AND HOLD UNDER ACR XAY CALL SIGN. YET HE (THE TWR CTLR) ALSO FAILED TO HEAR OUR CALL SIGN OF ACR XYZ RESPONDING TO THE INITIAL CLRNC TO TAXI INTO POS AND HOLD. WE WERE THEN PROPERLY CLRED FOR TKOF WITH OUR CORRECT CALL SIGN WITH NO FURTHER IRREGULARITIES. IT IS QUITE APPARENT THAT I (CAPT) SHOULD HAVE CAUGHT THE ERROR AT THE TIME THAT IT OCCURRED. HAD I DONE SO; BEFORE TAKING THE RWY; THIS VERBAL COM BREAKDOWN WOULD NEVER HAVE OCCURRED. FORTUNATELY THE PROB WAS CORRECTED IN A VERY SHORT PERIOD OF TIME AND THE FLT CONTINUED ON TO ITS DEST SAFELY.