B737 TAXIING FOR DEP AT LAS CROSSED RWY HOLD LINE. EVENTUALLY WAS ABLE TO ADVISE LAS TWR; WHO CONTINUED TO ISSUE A LNDG AND DEP CLRNC.

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HOLDING SHORT OF RWY 19L AT TXWY D; WE RECEIVED CLRNC INTO POS AND HOLD. WE REPEATED THE CLRNC; AND BEGAN TO TAXI. AFTER A FEW SECONDS; THE TWR SAID; 'ACR X HOLD SHORT OF THE RWY' AND CLRED A PVT JET FOR TKOF FROM THE OPPOSITE SIDE OF THE RWY. WE IMMEDIATELY STOPPED THE ACFT; BUT WE WERE PAST THE HOLD SHORT LINE APPROX 15 FT. WE MADE SEVERAL ATTEMPTS TO RELAY THIS INFO TO THE TWR; BUT KEPT GETTING STEPPED ON. THE RADIOS WERE VERY BUSY. WE FINALLY GOT THROUGH TO THE TWR AND TOLD THEM THAT THEY HAD CLRED US INTO POS; THEN RESCINDED THE CLRNC; BUT NOT IN TIME FOR US TO STOP SHORT OF THE HOLD SHORT LINE. WE ALSO SAID THAT WE WERE PAST THE LINE ABOUT 15 FT. THE TWR THEN SAID; 'NO PROB; JUST REMAIN CLR OF THE RWY;' AND THEY CLRED ANOTHER ACFT TO LAND. AFTER THIS ARR; WE WERE CLRED FOR TKOF AND DEPARTED LAS VEGAS. I THINK WHAT PROBABLY HAPPENED WAS THAT THE TWR NEVER HEARD OUR ACCEPTANCE OF THE 'INTO POS AND HOLD' CLRNC; SO THEY DECIDED TO LET ANOTHER ACFT DEPART IN FRONT OF US BUT WAITED TOO LONG TO TELL US TO REMAIN HOLDING SHORT. WHATEVER THE REASON; THE TWR INDICATED TO US THAT WE HAD DONE NOTHING WRONG. SO; I FEEL THAT THERE WAS NO FAR VIOLATION ON OUR PART; BUT THERE WAS A PROCEDURAL DEV SIMPLY BECAUSE OF THE FACT THAT ONE ACFT DEPARTED AND ONE LANDED WHILE WE WERE PAST THE HOLD SHORT LINE.