DHC8 FLT CREW HAD A RWY INCURSION ON RWY 8L AT HNL.

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AT APPROX XA35 LCL TIME IN HAWAII; ACR X HAD TAXIED UP TO AND HELD SHORT OF RWY 8L AT TXWY L AT HNL. ACR Y; A B717 WAS GIVEN THE CLRNC 'RWY 8L POS AND HOLD' AT THE FULL LENGTH OF RWY 8L. IT IS A COMMON PRACTICE AT HNL TO SEND ANOTHER ACFT INTO POS AND HOLD FURTHER DOWN THE RWY. SHORTLY AFTER ACR Y'S CLRNC; TO THE BEST OF BOTH MY KNOWLEDGE AND THAT OF MY FO; TWR CLRED 'ACR X' INTO POS AND HOLD. MY FO READ BACK THE CLRNC; WE VISUALLY CHKED THE RWY NOTING THE B717 HOLDING IN POS AND PROCEEDED ONTO RWY 8L AT TXWY L AND INTO POS. WE STOPPED THE ACFT IN POS; SET THE PARKING BRAKE AND HELD. APPROX 10-15 SECONDS AFTER READING BACK OUR CLRNC; TWR ADVISED THAT 'ACR X' HAD NOT BEEN CLRED ONTO THE RWY. AT SOME POINT THE ACR Y FLT HAD BEEN CLRED FOR TKOF WHICH NEITHER THE FO OR MYSELF HEARD. TWR ADVISED THAT FLT TO CANCEL TKOF CLRNC. I CALLED THE TWR AND ASKED IF THEY WANTED US TO CLR THE RWY AND THEY RESPONDED AFFIRMATIVELY. TWR STATED THAT THE POS AND HOLD CLRNC WHICH WE ACCEPTED WAS IN FACT MEANT FOR A SIMILAR CALL SIGN 'ACR Z.' CLRING THE RWY WE CONTACTED GND CTL; TAXIED BACK TO RWY 8L AT TXWY L AND DEPARTED SHORTLY AFTERWARD. NO MENTION OF THE MISCOM/RWY INCURSION WAS MADE BY ATC THAT DAY. I CONFERRED WITH MY FO AND WE EACH BELIEVE THAT WE HEARD 'ACR X' AND NOT 'ACR Z' GIVEN THE POS AND HOLD CLRNC. NOTHING WAS SAID BY TWR REGARDING OUR READBACK OF THE CLRNC OR TAXI ONTO THE RWY UNTIL WE HAD ALREADY REACHED POS AND STOPPED THE ACFT ON THE RWY. I BELIEVE THAT THE FORE MENTIONED EVENT TOOK PLACE BECAUSE OF CONFUSION REGARDING THE SIMILAR SOUNDING FLT NUMBERS X AND Z. I WOULD SUGGEST THAT DISTINCT EMPHASIS BE PLACED ON THE CALL SIGN AND FLT NUMBER WHENEVER SIMILAR SOUNDING FLTS EXIST AND THAT THE CREWS OF THOSE FLTS BE ADVISED OF THE SIT. OFTENTIMES WE ARE ADVISED OF A SIMILAR SOUNDING CALL SIGN BUT NOT IN THIS CASE. IN ADDITION TO THE X CALL SIGN; THERE IS A 'W' AND AN 'XX.' DUE TO DIFFERENCES IN INDIVIDUAL CTLRS' AND PLTS' VOICES EVEN ACR Z AND ACR YY HAVE AT TIMES SOUNDED SIMILAR TO ACR X. I WILL ALSO SUGGEST TO MY COMPANY THAT OUR CALL SIGN BE CHANGED TO A MORE DISTINCT SEPARATE NAME RATHER THAN ACR X.