SD3-60 FLT CREW ENTERS RWY AT ONT WITHOUT CLRNC AND CAUSES GAR.

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WE WERE HOLDING SHORT OF TXWY SIERRA ON TXWY WHISKY AS WE ADVISED TWR THAT WE WERE READY FOR DEP. WE BELIEVED WE HAD BEEN INSTRUCTED TO TAXI UP AND HOLD ON RWY 26L. MY FO READ THE INSTRUCTIONS AND REPLIED TAXI UP AND HOLD ON RWY 26. TWR REPLIED BACK AND SAID RWY 26L. MY FO AND I AT THAT POINT UNDERSTOOD THAT THE INSTRUCTION WAS INDEED FOR US TO TAXI AND HOLD ON RWY 26L. AGAIN; MY FO READ BACK THE INSTRUCTIONS TO TAXI UP AND HOLD ON RWY 26L; BUT THERE WAS NO RESPONSE FROM TWR AT THIS TIME. WE ASSUMED EVERYTHING WAS RIGHT; WENT AHEAD AND LINED UP AND HOLD ON RWY 26L. WHILE TAXIING UP; WE WERE AWARE THAT TWR CLRED A LNDG TFC ON RWY 26L. WHILE HOLDING ON RWY 26L; I TOLD MY FO TO REMIND TWR THAT WE WERE HOLDING ON RWY 26L. TWR VERIFIED OUR POS AND THEREAFTER INSTRUCTED THE LNDG TFC TO GAR. WE WERE THEN INSTRUCTED TO TAXI OUT THE RWY AND EXIT ON TXWY TANGO. WE STAYED ON TXWY SIERRA UNTIL WE GOT OUR TAKEOFF CLRNC. UPON AIRBORNE AND JUST BEFORE WE SWITCHED TO SOCAL DEP; WE WERE TOLD BY TWR TO CALL A PHONE NUMBER AFTER WE LAND IN IPL (IMPERIAL; CA). I CALLED UP THE NUMBER AND WAS ABLE TO TALK TO THE ATC MANAGER IN ONTARIO. HE TOLD ME WHAT TRANSPIRED EARLIER ON IN ONT. HE SAID THAT THE INSTRUCTIONS WERE FOR US TO TAXI UP AND HOLD SHORT OF RWY 26L. TWR'S RESPONSE TO OUR FIRST READBACK WAS INDEED ONLY RWY 26L. THERE WAS NO RESPONSE FROM TWR TO OUR SECOND READBACK APPARENTLY BECAUSE ACCORDING TO THE ATC MANAGER; WE WERE STEPPED ON. WE HOWEVER; DID NOT KNOW. WE DID NOT HEAR ANY OTHER TRANSMITTING WHEN WE MADE OUR LAST RADIO CALL TO TWR TO CONFIRM/READ BACK THE INSTRUCTIONS. OBVIOUSLY; COM WAS THE MAJOR FAULT IN THE ABOVE MENTIONED OF EVENTS. VIGILANCE AND AGGRESSIVENESS SHALL ALWAYS BE EXERCISED. PHRASEOLOGY SHOULD BE STANDARD AT ALL TIMES AND READING BACK OF INSTRUCTIONS COULDN'T BE OVEREMPHASIZED.