SIMILAR CALL SIGNS AND POOR COMS CAUSE POSSIBLE RWY INCURSION.

Narrative

TAXIING TO RWY 17L PRIOR TO THE HOLD SHORT LINE TWR CLRED OUR FLT FOR TKOF. THE FO RESPONDED THAT WE NEEDED 2 MINS FOR ENG WARM-UP. THE TWR THEN TOLD OUR FLT TO HOLD SHORT. THE FO RESPONDED TO TWR AND WE HELD SHORT OF RWY 17L. I THEN TOLD THE FO TO TELL TWR THAT WE WERE READY FOR TKOF. WE DID NOT NEED THE 2 MIN DELAY FOR ENG WARM-UP. I THEN HEARD THE TWR SAY 'ACR XXX; CLRED FOR TKOF.' THE FO RESPONDED; 'ROGER; ACR XXX; CLRED FOR TKOF.' I THEN THINK TWR SAID; 'ACR YYY; CANCEL TKOF CLRNC.' I STOPPED THE ACFT. I WAS STILL ON THE HOLD SHORT LINE. I THEN HEARD ACR YYY SAY; 'THE OTHER ACFT THINKS HE HAS TKOF CLRNC. 'THE TWR THEN SAID; 'ACR XXX; YOU ARE CLRED FOR TKOF.' THE OTHER ACR YYY ACFT'S CALL SIGN WAS 'ACR YYY.' TWR APPARENTLY HAD CLRED 'ACR YYY FOR TKOF ON RWY 17L. I HEARD 'ACR XXX CLRED FOR TKOF;' AND THE FO RESPONDED TO THIS. EVEN AFTER WE ENSURED WE WERE CORRECTLY CLRED FOR TKOF; THE TWR STILL DID NOT SOUND LIKE HE WAS SAYING 'ACR YYY' TO ME UNTIL HE MADE AN EFFORT TO FORCEFULLY ENUNCIATE THE WORD 'ACR YYY.' IT SOUNDED TO ME THAT TWR WAS NOT KEYING HIS MIKE UNTIL THE END OF SAYING 'ACR.' THE PROB OF SIMILAR CALL SIGNS REMAINS A CONSTANT SOURCE OF CONFUSION.