ACR TAXIES ONTO RWY AT DFW; TX; WITHOUT CLRNC AND STILL ON GND CTL FREQ.

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WHEN WE CHKED ON TO GND CTL W ON TOP OF ZULU BRIDGE; CTLR ASKED IF WE HAD OUR CLOSEOUT. WE REPLIED YES. WE FELT THE CTLR THEN SAID TAXI INTO POS RWY 18L. I BELIEVE THE FO REPEATED THIS. THE FO EVEN COMMENTED TO ME THAT THE CTLR MUST BE CANADIAN SINCE HE SAID INTO POS INSTEAD OF POS AND HOLD. WITH THAT INFO; WE COMPLETED THE BEFORE TKOF CHKLIST AND WENT INTO POS ON RWY 18L. AS WE DID SO; THE GND CTLR STATED 'ACR X YOU NEED TO TALK TO TWR.' WE THEN REALIZED THAT WE WERE STILL ON GND CTL FREQ. I TRULY FELT THAT WE HAD BEEN CLRED INTO POS ON THE RWY. THERE IS; HOWEVER; NO EXCUSE FOR NOT REALIZING WE WERE TAKING POS ON THE RWY WITHOUT BEING ON TWR FREQ AND QUESTIONING THE CTLR'S NOT GIVING US A POS AND HOLD CLRNC. SUPPLEMENTAL INFO FROM ACN 473330: LOCATION: DFW AT TXWY Z AND RWY 18R. WE WERE GIVEN THE RWY 18L BRIDGE TAXI CLRNC BY GND ON 121.85. UPON REACHING THE ZULU BRIDGE I SWITCHED TO W GND ON 121.85 AND CHKED IN. THE W GND ASKED IF WE WERE READY FOR DEP WITH ALL NUMBERS AND CLOSEOUT. WE ACKNOWLEDGED THAT WE WERE AND AT THAT POINT GND ISSUED A STATEMENT THAT I INTERPED AS CLRED INTO POS. WE SHOULD HAVE QUESTIONED THE STATEMENT; BUT NEITHER OF US DID. ALSO; THE FACT THAT WE SWITCHED FROM ONE GND FREQ TO ANOTHER REINFORCED THE HABIT PATTERN OF GOING FROM GND TO TWR. THE QUESTIONS ASKED BY GND ON THE SECOND FREQ SOUNDED LIKE TWR QUESTIONS AND I SIMPLY LET MYSELF GO DOWN THE HABIT PATTERN PATH. I DID ACKNOWLEDGE THE INSTRUCTIONS AS I INTERPED THEM AND DID NOT GET ANY FURTHER RESPONSE FROM GND. WE CLRED BOTH ENDS OF THE RWY AND SLOWLY TAXIED INTO POS. IT WAS THEN THAT GND SAID THE TWR WANTED TO TALK WITH US AND WE THEN REALIZED WE WERE STILL ON THE GND FREQ. WE CONTACTED TWR AND THEY CLRED US FOR TKOF.