ACR X RESPONSE TO WRONG CALL SIGN RWY INCURSION TKOF ON OCCUPIED RWY OPPOSITE DIRECTION TFC HAD LTSS FROM Y.

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ACR X CALLED GND CTL FOR TAXI REQUESTING RWY 8R. THE TWR WAS JUST CHANGING RWYS TO RWY 26L/R. WE WERE CLRED TO RWY 8R AT INTXN 42 TO HOLD SHORT FOR TKOF CLRNC. ALL CHKLISTS WERE COMPLETED AND THE TWR WAS NOTIFIED THAT ACR X WAS READY FOR TKOF AT RWY 8R. X WAS CLRED FOR TKOF ON RWY 8R. I REPEATED BACK TO THE TWR 'X CLRED FOR TKOF RWY 8R.' THE CAPT SET THE MAX PWR AND I; THE FO; WAS GIVEN CTL OF THE ACFT. I WATCHED TO ENSURE THE PWR WAS SET AND LOOKED DOWN THE RWY; WHEN I REALIZED THAT THERE WERE LIGHTS AT THE FAR END OF THE RWY FROM AN ACFT ON THE RWY AT THE OPPOSITE END (RWY 26L). I SAID 'JESUS; LIGHTS; ABORT.' THE CAPT REJECTED THE TKOF AND I CALLED THE TWR 'X IS ABORTING.' WE EXITED AT TXWY 54 (APPROX 2200 FT FROM OUR TKOF POINT). A CESSNA CARAVAN WAS TAKING OFF AT THE SAME TIME IN THE OPPOSITE DIRECTION ON RWY 26L. ONTARIO TWR REQUESTED THAT THE CARAVAN DISCONTINUE THE TKOF BUT HE WAS ALREADY AIRBORNE. HE BANKED TO THE R AND CLRED US BY ABOUT 500 FT IN ALT AND WAS AT LEAST 6000 FT DOWN THE RWY WHEN WE EXITED. WE WERE TOLD TO TAXI BACK TO RWY 8R AT TXWY 42 TO HOLD SHORT FOR TKOF. WE WERE ASKED TO CONTACT THE ONTARIO SUPVR ON THE TELEPHONE WHEN WE ARRIVED AT OUR DEST OF MEMPHIS; TN. UPON ARR IN MEMPHIS; THE CAPT CONTACTED ONTARIO TWR AND HE WAS TOLD THAT PAPERS WERE FILED ABOUT THE INCIDENT. THE TWR STATED THAT DIFFERENT COMPANY SAME NUMBERS WAS ON RWY 26R AND THAT WAS THE ACFT CLRED FOR TKOF; NOT ACR X. I BELIEVE THIS INCIDENT OCCURRED BECAUSE ANOTHER ACFT WITH THE SAME CALL SIGN WAS AWAITING TKOF ON THE OTHER RWY (RWY 26R). THE ARPT WAS ALSO USING 3 DIFFERENT RWYS AT THE SAME TIME. WE TOOK THE CORRECT AND APPROPRIATE ACTION WHEN I SAW THE ACFT LIGHTS FROM THE CARAVAN AND REJECTED THE TKOF. TO PREVENT AN OCCURRENCE OF THIS NATURE; WHEN USING OPPOSING RWYS THE TWR SHOULD EXERCISE EXTREME CAUTION FOR MISCOM. WHEN LIKE CALL SIGNS ARE IN USE ON THE SAME FREQ; THE TWR SHOULD ENSURE THAT BOTH ACFT ARE ADVISED OF THE LIKE CALL SIGNS. SUPPLEMENTAL INFO FROM ACN 284422: SMA Y WAS CLRED FOR TKOF ON RWY 26L AND THE B-727 WAS HOLDING RWY 8R; AND HAD TAKEN A TKOF CLRNC FROM THE ACFT CLRED ON RWY 26R.