EMB135 CREW HAD A RWY INCURSION AT ORD AFTER THE CREW WAS GIVEN THE WRONG LCL CTLR FREQ; AND THEN TOOK A 'POS AND HOLD' CLRNC INTENDED FOR ANOTHER COMPANY ACFT.

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WE WERE CLRED TO TAXI TO RWY 27L BY FOLLOWING COMPANY ACFT. WE FOLLOWED COMPANY TO THE RWY WHERE THAT ACFT DID A 270 DEG TURN. WHEN WE CALLED THE TWR TO ASK WHAT WAS HAPPENING THEY TOLD US THAT WE WERE GIVEN THE WRONG FREQ. WE SWITCHED OVER TO THE NEW TWR FREQ AND CHKED IN. HE ASKED IF WE WERE READY TO GO. I SAID 1 MIN AND CLICKED OVER TO THE PA TO MAKE THE DEP ANNOUNCEMENT. WHEN I CAME BACK TO COM1; I HEARD THE END OF THE CAPT'S CALL SAYING THAT WE WERE READY. THE CTLR CAME BACK WITH A TAXI INTO POS AND HOLD ON RWY 27L. I READ BACK THE POS AND HOLD CLRNC ALONG WITH OUR FLT NUMBER. WE WERE ON THE RWY FOR ABOUT 30 SECONDS WHEN THE TWR CTLR CLRED US FOR TKOF USING THE OTHER FLT'S NUMBER. HE TOLD US THAT HE WOULD WORK IT OUT. THE THING I REMEMBER IS THAT AFTER WE WENT TO TAXI ONTO THE RWY THE OTHER COMPANY FLT THAT WE WERE NOSE TO NOSE WITH NEVER MOVED. HAD THEY EVEN BEGUN TO TAXI; WE WOULD HAVE THOUGHT THAT 1 OF US WAS MISTAKEN. I BELIEVE THE CTLR GOT THE WRONG STRIP AND SENT US INTO POS. I WAS ABOUT TO OFFER FOR US TO TURN OFF THE RWY WHEN HE CLRED US FOR TKOF. THERE WAS NO FURTHER INCIDENT.