AN ACR CKP INADVERTENTLY ENTERED THE WRONG ACFT NUMBER IN THE ACAR PDC RESULTING IN THE ACFT DEPARTING WITH A CLRNC FOR ANOTHER ACFT.

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I WAS A CAPT UNDER TRAINING WITH AN INSTRUCTOR PLT ON AN MLG. WE WERE PREPARING TO DEPART PHL FOR AN IFR FLT TO DTW WITH REVENUE PAX ON BOARD THE ACFT. THE INSTRUCTOR HAD ENTERED THE WRONG FLT NUMBER IN THE ACARS UNIT AND THEREFORE RECEIVED THE WRONG IFR CLRNC VIA THE ACARS. WE HAD THE CORRECT FLT PLAN ON OUR COMPANY RELEASE AND THE CORRECT FLT PLAN ENTERED IN OUR FMS FOR THE FLT TO DTW. TAXI AND TKOF WERE NORMAL BUT ONCE INFLT REALIZED THAT WE HAD THE WRONG DEP FREQ AND XPONDER CODE. THOSE 2 ERRORS ALERTED US TO OUR ERROR. WE CALLED BACK TO PHL CLRNC DELIVERY WITHIN MINS OF OUR TKOF AND EXPLAINED THE ERROR. (THE WRONG FLT NUMBER IN THE ACARS UNIT.) WE CONFIRMED OUT CORRECT ROUTING AND XPONDER CODE. ONCE AGAIN; THE CORRECT RTE WAS ALREADY IN THE FMS AND BEING FLOWN AS EXPECTED. THERE WAS NO PROB BECAUSE THE FMS HAD BEEN PROGRAMMED CORRECTLY. THE ONLY PROB WAS OF A TECHNICAL NATURE; I.E.; WE HAD RECEIVED THE WRONG CLRNC VIA ACARS. FROM THE TIME WE TAXIED OUT; WE USED OUR CORRECT FLT NUMBER THROUGHOUT THE FLT. TWR CLRED US FOR TKOF WITH OUR CORRECT FLT NUMBER. I WONDERED LATER WHY THE TWR STRIP ON US DID NOT SHOW THAT OUR CORRECT IFR CLRNC HAD NOT BEEN XMITTED TO US EITHER VIA ACARS OR VIA VHF RADIO XMISSION. THE INSTRUCTOR PLT CALLED PHL TRACON THE NEXT DAY WHEN WE WERE IN PHL AGAIN. A SHIFT SUPVR REMEMBERED THE SIT AND SAID IT HAPPENS OCCASIONALLY AND THAT NO PROB WAS CREATED BY THE CLRNC MIXUP. CLOSER ATTN BY ME OR ANY CREW WOULD HAVE CAUGHT THE ERROR PRIOR TO LEAVING THE GATE.